diff --git a/docs/assets/ttt/ttt-23-02-02-sm_hanger.py b/docs/assets/ttt/ttt-23-02-02-sm_hanger.py
index b523175d..309f61f8 100644
--- a/docs/assets/ttt/ttt-23-02-02-sm_hanger.py
+++ b/docs/assets/ttt/ttt-23-02-02-sm_hanger.py
@@ -92,6 +92,13 @@
     mirror(about=Plane.YZ)
     mirror(about=Plane.XZ)
 
-print(f"Mass: {sm_hanger.part.volume*7800*1e-6:0.1f} g")
+got_mass = sm_hanger.part.volume*7800*1e-6
+want_mass = 1028
+tolerance = 10
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.1f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
+
+assert abs(got_mass - 1028) < 10, f'{got_mass=}, want=1028, tolerance=10'
 
 show(sm_hanger)
diff --git a/docs/assets/ttt/ttt-23-t-24-curved_support.py b/docs/assets/ttt/ttt-23-t-24-curved_support.py
index 26b469b2..d54f6ee8 100644
--- a/docs/assets/ttt/ttt-23-t-24-curved_support.py
+++ b/docs/assets/ttt/ttt-23-t-24-curved_support.py
@@ -27,7 +27,7 @@
     (yl8 - 50) / (55 / 2 - xl8) - tan(radians(8)),  # 8 degree slope
 ]
 # There are two solutions but we want the 2nd one
-solution = sympy.solve(equations, dict=True)[1]
+solution = {k: float(v) for k,v in sympy.solve(equations, dict=True)[1].items()}
 
 # Create the critical points
 c30 = Vector(x30, solution[y30])
@@ -58,5 +58,11 @@
     with Locations((0, 125)):
         Hole(20 / 2)
 
-print(curved_support.part.volume * 7800e-6)
+got_mass = curved_support.part.volume * 7800e-6
+want_mass = 1294
+delta = abs(got_mass - want_mass)
+tolerance = 3
+print(f"Mass: {got_mass:0.1f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
+
 show(curved_support)
diff --git a/docs/assets/ttt/ttt-24-SPO-06-Buffer_Stand.py b/docs/assets/ttt/ttt-24-SPO-06-Buffer_Stand.py
index a54d77c1..60c0fce7 100644
--- a/docs/assets/ttt/ttt-24-SPO-06-Buffer_Stand.py
+++ b/docs/assets/ttt/ttt-24-SPO-06-Buffer_Stand.py
@@ -45,6 +45,13 @@
     mirror(about=Plane.YZ)
 
 part = scale(p.part, IN)
-print(f"\npart weight = {part.volume*7800e-6/LB:0.2f} lbs")
+
+
+got_mass = part.volume*7800e-6/LB
+want_mass = 3.923
+tolerance = 0.02
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.1f} lbs")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
 
 show(p)
diff --git a/docs/assets/ttt/ttt-ppp0101.py b/docs/assets/ttt/ttt-ppp0101.py
index 8a78180e..efd0a27f 100644
--- a/docs/assets/ttt/ttt-ppp0101.py
+++ b/docs/assets/ttt/ttt-ppp0101.py
@@ -1,47 +1,54 @@
-"""
-Too Tall Toby Party Pack 01-01 Bearing Bracket
-"""
-
-from build123d import *
-from ocp_vscode import *
-
-densa = 7800 / 1e6  # carbon steel density g/mm^3
-densb = 2700 / 1e6  # aluminum alloy
-densc = 1020 / 1e6  # ABS
-
-with BuildPart() as p:
-    with BuildSketch() as s:
-        Rectangle(115, 50)
-        with Locations((5 / 2, 0)):
-            SlotOverall(90, 12, mode=Mode.SUBTRACT)
-    extrude(amount=15)
-
-    with BuildSketch(Plane.XZ.offset(50 / 2)) as s3:
-        with Locations((-115 / 2 + 26, 15)):
-            SlotOverall(42 + 2 * 26 + 12, 2 * 26, rotation=90)
-    zz = extrude(amount=-12)
-    split(bisect_by=Plane.XY)
-    edgs = p.part.edges().filter_by(Axis.Y).group_by(Axis.X)[-2]
-    fillet(edgs, 9)
-
-    with Locations(zz.faces().sort_by(Axis.Y)[0]):
-        with Locations((42 / 2 + 6, 0)):
-            CounterBoreHole(24 / 2, 34 / 2, 4)
-    mirror(about=Plane.XZ)
-
-    with BuildSketch() as s4:
-        RectangleRounded(115, 50, 6)
-    extrude(amount=80, mode=Mode.INTERSECT)
-    # fillet does not work right, mode intersect is safer
-
-    with BuildSketch(Plane.YZ) as s4:
-        with BuildLine() as bl:
-            l1 = Line((0, 0), (18 / 2, 0))
-            l2 = PolarLine(l1 @ 1, 8, 60, length_mode=LengthMode.VERTICAL)
-            l3 = Line(l2 @ 1, (0, 8))
-            mirror(about=Plane.YZ)
-        make_face()
-    extrude(amount=115/2, both=True, mode=Mode.SUBTRACT)
-
-show_object(p)
-print(f"\npart mass = {p.part.volume*densa:0.2f}")
+"""
+Too Tall Toby Party Pack 01-01 Bearing Bracket
+"""
+
+from build123d import *
+from ocp_vscode import *
+
+densa = 7800 / 1e6  # carbon steel density g/mm^3
+densb = 2700 / 1e6  # aluminum alloy
+densc = 1020 / 1e6  # ABS
+
+with BuildPart() as p:
+    with BuildSketch() as s:
+        Rectangle(115, 50)
+        with Locations((5 / 2, 0)):
+            SlotOverall(90, 12, mode=Mode.SUBTRACT)
+    extrude(amount=15)
+
+    with BuildSketch(Plane.XZ.offset(50 / 2)) as s3:
+        with Locations((-115 / 2 + 26, 15)):
+            SlotOverall(42 + 2 * 26 + 12, 2 * 26, rotation=90)
+    zz = extrude(amount=-12)
+    split(bisect_by=Plane.XY)
+    edgs = p.part.edges().filter_by(Axis.Y).group_by(Axis.X)[-2]
+    fillet(edgs, 9)
+
+    with Locations(zz.faces().sort_by(Axis.Y)[0]):
+        with Locations((42 / 2 + 6, 0)):
+            CounterBoreHole(24 / 2, 34 / 2, 4)
+    mirror(about=Plane.XZ)
+
+    with BuildSketch() as s4:
+        RectangleRounded(115, 50, 6)
+    extrude(amount=80, mode=Mode.INTERSECT)
+    # fillet does not work right, mode intersect is safer
+
+    with BuildSketch(Plane.YZ) as s4:
+        with BuildLine() as bl:
+            l1 = Line((0, 0), (18 / 2, 0))
+            l2 = PolarLine(l1 @ 1, 8, 60, length_mode=LengthMode.VERTICAL)
+            l3 = Line(l2 @ 1, (0, 8))
+            mirror(about=Plane.YZ)
+        make_face()
+    extrude(amount=115/2, both=True, mode=Mode.SUBTRACT)
+
+show_object(p)
+
+
+got_mass = p.part.volume*densa
+want_mass = 797.15
+tolerance = 1
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.2f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
diff --git a/docs/assets/ttt/ttt-ppp0102.py b/docs/assets/ttt/ttt-ppp0102.py
index df1df563..96703148 100644
--- a/docs/assets/ttt/ttt-ppp0102.py
+++ b/docs/assets/ttt/ttt-ppp0102.py
@@ -1,49 +1,57 @@
-"""
-Too Tall Toby Party Pack 01-02 Post Cap
-"""
-
-from build123d import *
-from ocp_vscode import *
-
-densa = 7800 / 1e6  # carbon steel density g/mm^3
-densb = 2700 / 1e6  # aluminum alloy
-densc = 1020 / 1e6  # ABS
-
-
-# TTT Party Pack 01: PPP0102, mass(abs) = 43.09g
-with BuildPart() as p:
-    with BuildSketch(Plane.XZ) as sk1:
-        Rectangle(49, 48 - 8, align=(Align.CENTER, Align.MIN))
-        Rectangle(9, 48, align=(Align.CENTER, Align.MIN))
-        with Locations((9 / 2, 40)):
-            Ellipse(20, 8)
-        split(bisect_by=Plane.YZ)
-    revolve(axis=Axis.Z)
-
-    with BuildSketch(Plane.YZ.offset(-15)) as xc1:
-        with Locations((0, 40 / 2 - 17)):
-            Ellipse(10 / 2, 4 / 2)
-        with BuildLine(Plane.XZ) as l1:
-            CenterArc((-15, 40 / 2), 17, 90, 180)
-    sweep(path=l1)
-
-    fillet(p.edges().filter_by(GeomType.CIRCLE, reverse=True).group_by(Axis.X)[0], 1)
-
-    with BuildLine(mode=Mode.PRIVATE) as lc1:
-        PolarLine(
-            (42 / 2, 0), 37, 94, length_mode=LengthMode.VERTICAL
-        )  # construction line
-
-    pts = [
-        (0, 0),
-        (42 / 2, 0),
-        ((lc1.line @ 1).X, (lc1.line @ 1).Y),
-        (0, (lc1.line @ 1).Y),
-    ]
-    with BuildSketch(Plane.XZ) as sk2:
-        Polygon(*pts, align=None)
-        fillet(sk2.vertices().group_by(Axis.X)[1], 3)
-    revolve(axis=Axis.Z, mode=Mode.SUBTRACT)
-
-show(p)
-print(f"\npart mass = {p.part.volume*densa:0.2f}")
+"""
+Too Tall Toby Party Pack 01-02 Post Cap
+"""
+
+from build123d import *
+from ocp_vscode import *
+
+densa = 7800 / 1e6  # carbon steel density g/mm^3
+densb = 2700 / 1e6  # aluminum alloy
+densc = 1020 / 1e6  # ABS
+
+
+# TTT Party Pack 01: PPP0102, mass(abs) = 43.09g
+with BuildPart() as p:
+    with BuildSketch(Plane.XZ) as sk1:
+        Rectangle(49, 48 - 8, align=(Align.CENTER, Align.MIN))
+        Rectangle(9, 48, align=(Align.CENTER, Align.MIN))
+        with Locations((9 / 2, 40)):
+            Ellipse(20, 8)
+        split(bisect_by=Plane.YZ)
+    revolve(axis=Axis.Z)
+
+    with BuildSketch(Plane.YZ.offset(-15)) as xc1:
+        with Locations((0, 40 / 2 - 17)):
+            Ellipse(10 / 2, 4 / 2)
+        with BuildLine(Plane.XZ) as l1:
+            CenterArc((-15, 40 / 2), 17, 90, 180)
+    sweep(path=l1)
+
+    fillet(p.edges().filter_by(GeomType.CIRCLE, reverse=True).group_by(Axis.X)[0], 1)
+
+    with BuildLine(mode=Mode.PRIVATE) as lc1:
+        PolarLine(
+            (42 / 2, 0), 37, 94, length_mode=LengthMode.VERTICAL
+        )  # construction line
+
+    pts = [
+        (0, 0),
+        (42 / 2, 0),
+        ((lc1.line @ 1).X, (lc1.line @ 1).Y),
+        (0, (lc1.line @ 1).Y),
+    ]
+    with BuildSketch(Plane.XZ) as sk2:
+        Polygon(*pts, align=None)
+        fillet(sk2.vertices().group_by(Axis.X)[1], 3)
+    revolve(axis=Axis.Z, mode=Mode.SUBTRACT)
+
+show(p)
+
+
+got_mass = p.part.volume*densc
+want_mass = 43.09
+tolerance = 1
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.2f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
+
diff --git a/docs/assets/ttt/ttt-ppp0103.py b/docs/assets/ttt/ttt-ppp0103.py
index b021b9b4..1465232b 100644
--- a/docs/assets/ttt/ttt-ppp0103.py
+++ b/docs/assets/ttt/ttt-ppp0103.py
@@ -1,34 +1,40 @@
-"""
-Too Tall Toby Party Pack 01-03 C Clamp Base
-"""
-
-from build123d import *
-from ocp_vscode import *
-
-densa = 7800 / 1e6  # carbon steel density g/mm^3
-densb = 2700 / 1e6  # aluminum alloy
-densc = 1020 / 1e6  # ABS
-
-
-with BuildPart() as ppp0103:
-    with BuildSketch() as sk1:
-        RectangleRounded(34 * 2, 95, 18)
-        with Locations((0, -2)):
-            RectangleRounded((34 - 16) * 2, 95 - 18 - 14, 7, mode=Mode.SUBTRACT)
-        with Locations((-34 / 2, 0)):
-            Rectangle(34, 95, 0, mode=Mode.SUBTRACT)
-    extrude(amount=16)
-    with BuildSketch(Plane.XZ.offset(-95 / 2)) as cyl1:
-        with Locations((0, 16 / 2)):
-            Circle(16 / 2)
-    extrude(amount=18)
-    with BuildSketch(Plane.XZ.offset(95 / 2 - 14)) as cyl2:
-        with Locations((0, 16 / 2)):
-            Circle(16 / 2)
-    extrude(amount=23)
-    with Locations(Plane.XZ.offset(95 / 2 + 9)):
-        with Locations((0, 16 / 2)):
-            CounterSinkHole(5.5 / 2, 11.2 / 2, None, 90)
-
-show(ppp0103)
-print(f"\npart mass = {ppp0103.part.volume*densb:0.2f}")
+"""
+Too Tall Toby Party Pack 01-03 C Clamp Base
+"""
+
+from build123d import *
+from ocp_vscode import *
+
+densa = 7800 / 1e6  # carbon steel density g/mm^3
+densb = 2700 / 1e6  # aluminum alloy
+densc = 1020 / 1e6  # ABS
+
+
+with BuildPart() as ppp0103:
+    with BuildSketch() as sk1:
+        RectangleRounded(34 * 2, 95, 18)
+        with Locations((0, -2)):
+            RectangleRounded((34 - 16) * 2, 95 - 18 - 14, 7, mode=Mode.SUBTRACT)
+        with Locations((-34 / 2, 0)):
+            Rectangle(34, 95, 0, mode=Mode.SUBTRACT)
+    extrude(amount=16)
+    with BuildSketch(Plane.XZ.offset(-95 / 2)) as cyl1:
+        with Locations((0, 16 / 2)):
+            Circle(16 / 2)
+    extrude(amount=18)
+    with BuildSketch(Plane.XZ.offset(95 / 2 - 14)) as cyl2:
+        with Locations((0, 16 / 2)):
+            Circle(16 / 2)
+    extrude(amount=23)
+    with Locations(Plane.XZ.offset(95 / 2 + 9)):
+        with Locations((0, 16 / 2)):
+            CounterSinkHole(5.5 / 2, 11.2 / 2, None, 90)
+
+show(ppp0103)
+
+got_mass = ppp0103.part.volume*densb
+want_mass = 96.13
+tolerance = 1
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.2f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
diff --git a/docs/assets/ttt/ttt-ppp0104.py b/docs/assets/ttt/ttt-ppp0104.py
index 685b483b..88361fa1 100644
--- a/docs/assets/ttt/ttt-ppp0104.py
+++ b/docs/assets/ttt/ttt-ppp0104.py
@@ -1,57 +1,64 @@
-"""
-Too Tall Toby Party Pack 01-04 Angle Bracket
-"""
-
-from build123d import *
-from ocp_vscode import *
-
-densa = 7800 / 1e6  # carbon steel density g/mm^3
-densb = 2700 / 1e6  # aluminum alloy
-densc = 1020 / 1e6  # ABS
-
-d1, d2, d3 = 38, 26, 16
-h1, h2, h3, h4 = 20, 8, 7, 23
-w1, w2, w3 = 80, 10, 5
-f1, f2, f3 = 4, 10, 5
-sloth1, sloth2 = 18, 12
-slotw1, slotw2 = 17, 14
-
-with BuildPart() as p:
-    with BuildSketch() as s:
-        Circle(d1 / 2)
-    extrude(amount=h1)
-    with BuildSketch(Plane.XY.offset(h1)) as s2:
-        Circle(d2 / 2)
-    extrude(amount=h2)
-    with BuildSketch(Plane.YZ) as s3:
-        Rectangle(d1 + 15, h3, align=(Align.CENTER, Align.MIN))
-    extrude(amount=w1 - d1 / 2)
-    # fillet workaround \/
-    ped = p.part.edges().group_by(Axis.Z)[2].filter_by(GeomType.CIRCLE)
-    fillet(ped, f1)
-    with BuildSketch(Plane.YZ) as s3a:
-        Rectangle(d1 + 15, 15, align=(Align.CENTER, Align.MIN))
-        Rectangle(d1, 15, mode=Mode.SUBTRACT, align=(Align.CENTER, Align.MIN))
-    extrude(amount=w1 - d1 / 2, mode=Mode.SUBTRACT)
-    # end fillet workaround /\
-    with BuildSketch() as s4:
-        Circle(d3 / 2)
-    extrude(amount=h1 + h2, mode=Mode.SUBTRACT)
-    with BuildSketch() as s5:
-        with Locations((w1 - d1 / 2 - w2 / 2, 0)):
-            Rectangle(w2, d1)
-    extrude(amount=-h4)
-    fillet(p.part.edges().group_by(Axis.X)[-1].sort_by(Axis.Z)[-1], f2)
-    fillet(p.part.edges().group_by(Axis.X)[-4].sort_by(Axis.Z)[-2], f3)
-    pln = Plane.YZ.offset(w1 - d1 / 2)
-    with BuildSketch(pln) as s6:
-        with Locations((0, -h4)):
-            SlotOverall(slotw1 * 2, sloth1, 90)
-    extrude(amount=-w3, mode=Mode.SUBTRACT)
-    with BuildSketch(pln) as s6b:
-        with Locations((0, -h4)):
-            SlotOverall(slotw2 * 2, sloth2, 90)
-    extrude(amount=-w2, mode=Mode.SUBTRACT)
-
-show(p)
-print(f"\npart mass = {p.part.volume*densa:0.2f}")
+"""
+Too Tall Toby Party Pack 01-04 Angle Bracket
+"""
+
+from build123d import *
+from ocp_vscode import *
+
+densa = 7800 / 1e6  # carbon steel density g/mm^3
+densb = 2700 / 1e6  # aluminum alloy
+densc = 1020 / 1e6  # ABS
+
+d1, d2, d3 = 38, 26, 16
+h1, h2, h3, h4 = 20, 8, 7, 23
+w1, w2, w3 = 80, 10, 5
+f1, f2, f3 = 4, 10, 5
+sloth1, sloth2 = 18, 12
+slotw1, slotw2 = 17, 14
+
+with BuildPart() as p:
+    with BuildSketch() as s:
+        Circle(d1 / 2)
+    extrude(amount=h1)
+    with BuildSketch(Plane.XY.offset(h1)) as s2:
+        Circle(d2 / 2)
+    extrude(amount=h2)
+    with BuildSketch(Plane.YZ) as s3:
+        Rectangle(d1 + 15, h3, align=(Align.CENTER, Align.MIN))
+    extrude(amount=w1 - d1 / 2)
+    # fillet workaround \/
+    ped = p.part.edges().group_by(Axis.Z)[2].filter_by(GeomType.CIRCLE)
+    fillet(ped, f1)
+    with BuildSketch(Plane.YZ) as s3a:
+        Rectangle(d1 + 15, 15, align=(Align.CENTER, Align.MIN))
+        Rectangle(d1, 15, mode=Mode.SUBTRACT, align=(Align.CENTER, Align.MIN))
+    extrude(amount=w1 - d1 / 2, mode=Mode.SUBTRACT)
+    # end fillet workaround /\
+    with BuildSketch() as s4:
+        Circle(d3 / 2)
+    extrude(amount=h1 + h2, mode=Mode.SUBTRACT)
+    with BuildSketch() as s5:
+        with Locations((w1 - d1 / 2 - w2 / 2, 0)):
+            Rectangle(w2, d1)
+    extrude(amount=-h4)
+    fillet(p.part.edges().group_by(Axis.X)[-1].sort_by(Axis.Z)[-1], f2)
+    fillet(p.part.edges().group_by(Axis.X)[-4].sort_by(Axis.Z)[-2], f3)
+    pln = Plane.YZ.offset(w1 - d1 / 2)
+    with BuildSketch(pln) as s6:
+        with Locations((0, -h4)):
+            SlotOverall(slotw1 * 2, sloth1, 90)
+    extrude(amount=-w3, mode=Mode.SUBTRACT)
+    with BuildSketch(pln) as s6b:
+        with Locations((0, -h4)):
+            SlotOverall(slotw2 * 2, sloth2, 90)
+    extrude(amount=-w2, mode=Mode.SUBTRACT)
+
+show(p)
+
+
+got_mass = p.part.volume*densa
+want_mass = 310
+tolerance = 1
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.2f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
diff --git a/docs/assets/ttt/ttt-ppp0105.py b/docs/assets/ttt/ttt-ppp0105.py
index bf5c020f..f5997368 100644
--- a/docs/assets/ttt/ttt-ppp0105.py
+++ b/docs/assets/ttt/ttt-ppp0105.py
@@ -1,30 +1,38 @@
-"""
-Too Tall Toby Party Pack 01-05 Paste Sleeve
-"""
-
-from build123d import *
-from ocp_vscode import *
-
-densa = 7800 / 1e6  # carbon steel density g/mm^3
-densb = 2700 / 1e6  # aluminum alloy
-densc = 1020 / 1e6  # ABS
-
-with BuildPart() as p:
-    with BuildSketch() as s:
-        SlotOverall(45, 38)
-        offset(amount=3)
-    with BuildSketch(Plane.XY.offset(133 - 30)) as s2:
-        SlotOverall(60, 4)
-        offset(amount=3)
-    loft()
-
-    with BuildSketch() as s3:
-        SlotOverall(45, 38)
-    with BuildSketch(Plane.XY.offset(133 - 30)) as s4:
-        SlotOverall(60, 4)
-    loft(mode=Mode.SUBTRACT)
-
-    extrude(p.part.faces().sort_by(Axis.Z)[0], amount=30)
-
-show(p)
-print(f"\npart mass = {p.part.volume*densc:0.2f}")
+"""
+Too Tall Toby Party Pack 01-05 Paste Sleeve
+"""
+
+from build123d import *
+from ocp_vscode import *
+
+densa = 7800 / 1e6  # carbon steel density g/mm^3
+densb = 2700 / 1e6  # aluminum alloy
+densc = 1020 / 1e6  # ABS
+
+with BuildPart() as p:
+    with BuildSketch() as s:
+        SlotOverall(45, 38)
+        offset(amount=3)
+    with BuildSketch(Plane.XY.offset(133 - 30)) as s2:
+        SlotOverall(60, 4)
+        offset(amount=3)
+    loft()
+
+    with BuildSketch() as s3:
+        SlotOverall(45, 38)
+    with BuildSketch(Plane.XY.offset(133 - 30)) as s4:
+        SlotOverall(60, 4)
+    loft(mode=Mode.SUBTRACT)
+
+    extrude(p.part.faces().sort_by(Axis.Z)[0], amount=30)
+
+show(p)
+
+
+got_mass = p.part.volume*densc
+want_mass = 57.08
+tolerance = 1
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.2f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
+
diff --git a/docs/assets/ttt/ttt-ppp0106.py b/docs/assets/ttt/ttt-ppp0106.py
index 38aef2a1..596a47ba 100644
--- a/docs/assets/ttt/ttt-ppp0106.py
+++ b/docs/assets/ttt/ttt-ppp0106.py
@@ -1,52 +1,58 @@
-"""
-Too Tall Toby Party Pack 01-06 Bearing Jig
-"""
-
-from build123d import *
-from ocp_vscode import *
-
-densa = 7800 / 1e6  # carbon steel density g/mm^3
-densb = 2700 / 1e6  # aluminum alloy
-densc = 1020 / 1e6  # ABS
-
-r1, r2, r3, r4, r5 = 30 / 2, 13 / 2, 12 / 2, 10, 6  # radii used
-x1 = 44  # lengths used
-y1, y2, y3, y4, y_tot = 36, 36 - 22 / 2, 22 / 2, 42, 69  # widths used
-
-with BuildSketch(Location((0, -r1, y3))) as sk_body:
-    with BuildLine() as l:
-        c1 = Line((r1, 0), (r1, y_tot), mode=Mode.PRIVATE)  # construction line
-        m1 = Line((0, y_tot), (x1 / 2, y_tot))
-        m2 = JernArc(m1 @ 1, m1 % 1, r4, -90 - 45)
-        m3 = IntersectingLine(m2 @ 1, m2 % 1, c1)
-        m4 = Line(m3 @ 1, (r1, r1))
-        m5 = JernArc(m4 @ 1, m4 % 1, r1, -90)
-        m6 = Line(m5 @ 1, m1 @ 0)
-    mirror(make_face(l.line), Plane.YZ)
-    fillet(sk_body.vertices().group_by(Axis.Y)[1], 12)
-    with Locations((x1 / 2, y_tot - 10), (-x1 / 2, y_tot - 10)):
-        Circle(r2, mode=Mode.SUBTRACT)
-    # Keyway
-    with Locations((0, r1)):
-        Circle(r3, mode=Mode.SUBTRACT)
-        Rectangle(4, 3 + 6, align=(Align.CENTER, Align.MIN), mode=Mode.SUBTRACT)
-
-with BuildPart() as p:
-    Box(200, 200, 22)  # Oversized plate
-    # Cylinder underneath
-    Cylinder(r1, y2, align=(Align.CENTER, Align.CENTER, Align.MAX))
-    fillet(p.edges(Select.NEW), r5)  # Weld together
-    extrude(sk_body.sketch, amount=-y1, mode=Mode.INTERSECT)  # Cut to shape
-    # Remove slot
-    with Locations((0, y_tot - r1 - y4, 0)):
-        Box(
-            y_tot,
-            y_tot,
-            10,
-            align=(Align.CENTER, Align.MIN, Align.CENTER),
-            mode=Mode.SUBTRACT,
-        )
-
-show(p)
-print(f"\npart mass = {p.part.volume*densa:0.2f}")
-print(p.part.bounding_box().size)
+"""
+Too Tall Toby Party Pack 01-06 Bearing Jig
+"""
+
+from build123d import *
+from ocp_vscode import *
+
+densa = 7800 / 1e6  # carbon steel density g/mm^3
+densb = 2700 / 1e6  # aluminum alloy
+densc = 1020 / 1e6  # ABS
+
+r1, r2, r3, r4, r5 = 30 / 2, 13 / 2, 12 / 2, 10, 6  # radii used
+x1 = 44  # lengths used
+y1, y2, y3, y4, y_tot = 36, 36 - 22 / 2, 22 / 2, 42, 69  # widths used
+
+with BuildSketch(Location((0, -r1, y3))) as sk_body:
+    with BuildLine() as l:
+        c1 = Line((r1, 0), (r1, y_tot), mode=Mode.PRIVATE)  # construction line
+        m1 = Line((0, y_tot), (x1 / 2, y_tot))
+        m2 = JernArc(m1 @ 1, m1 % 1, r4, -90 - 45)
+        m3 = IntersectingLine(m2 @ 1, m2 % 1, c1)
+        m4 = Line(m3 @ 1, (r1, r1))
+        m5 = JernArc(m4 @ 1, m4 % 1, r1, -90)
+        m6 = Line(m5 @ 1, m1 @ 0)
+    mirror(make_face(l.line), Plane.YZ)
+    fillet(sk_body.vertices().group_by(Axis.Y)[1], 12)
+    with Locations((x1 / 2, y_tot - 10), (-x1 / 2, y_tot - 10)):
+        Circle(r2, mode=Mode.SUBTRACT)
+    # Keyway
+    with Locations((0, r1)):
+        Circle(r3, mode=Mode.SUBTRACT)
+        Rectangle(4, 3 + 6, align=(Align.CENTER, Align.MIN), mode=Mode.SUBTRACT)
+
+with BuildPart() as p:
+    Box(200, 200, 22)  # Oversized plate
+    # Cylinder underneath
+    Cylinder(r1, y2, align=(Align.CENTER, Align.CENTER, Align.MAX))
+    fillet(p.edges(Select.NEW), r5)  # Weld together
+    extrude(sk_body.sketch, amount=-y1, mode=Mode.INTERSECT)  # Cut to shape
+    # Remove slot
+    with Locations((0, y_tot - r1 - y4, 0)):
+        Box(
+            y_tot,
+            y_tot,
+            10,
+            align=(Align.CENTER, Align.MIN, Align.CENTER),
+            mode=Mode.SUBTRACT,
+        )
+
+show(p)
+
+
+got_mass = p.part.volume*densa
+want_mass = 328.02
+tolerance = 1
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.2f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
diff --git a/docs/assets/ttt/ttt-ppp0107.py b/docs/assets/ttt/ttt-ppp0107.py
index ca13804b..1ddc680e 100644
--- a/docs/assets/ttt/ttt-ppp0107.py
+++ b/docs/assets/ttt/ttt-ppp0107.py
@@ -1,52 +1,59 @@
-"""
-Too Tall Toby Party Pack 01-07 Flanged Hub
-"""
-
-from build123d import *
-from ocp_vscode import *
-
-densa = 7800 / 1e6  # carbon steel density g/mm^3
-densb = 2700 / 1e6  # aluminum alloy
-densc = 1020 / 1e6  # ABS
-
-with BuildPart() as p:
-    with BuildSketch() as s:
-        Circle(130 / 2)
-    extrude(amount=8)
-    with BuildSketch(Plane.XY.offset(8)) as s2:
-        Circle(84 / 2)
-    extrude(amount=25 - 8)
-    with BuildSketch(Plane.XY.offset(25)) as s3:
-        Circle(35 / 2)
-    extrude(amount=52 - 25)
-    with BuildSketch() as s4:
-        Circle(73 / 2)
-    extrude(amount=18, mode=Mode.SUBTRACT)
-    pln2 = p.part.faces().sort_by(Axis.Z)[5]
-    with BuildSketch(Plane.XY.offset(52)) as s5:
-        Circle(20 / 2)
-    extrude(amount=-52, mode=Mode.SUBTRACT)
-    fillet(
-        p.part.edges()
-        .filter_by(GeomType.CIRCLE)
-        .sort_by(Axis.Z)[2:-2]
-        .sort_by(SortBy.RADIUS)[1:],
-        3,
-    )
-    pln = Plane(pln2)
-    pln.origin = pln.origin + Vector(20 / 2, 0, 0)
-    pln = pln.rotated((0, 45, 0))
-    pln = pln.offset(-25 + 3 + 0.10)
-    with BuildSketch(pln) as s6:
-        Rectangle((73 - 35) / 2 * 1.414 + 5, 3)
-    zz = extrude(amount=15, taper=-20 / 2, mode=Mode.PRIVATE)
-    zz2 = split(zz, bisect_by=Plane.XY.offset(25), mode=Mode.PRIVATE)
-    zz3 = split(zz2, bisect_by=Plane.YZ.offset(35 / 2 - 1), mode=Mode.PRIVATE)
-    with PolarLocations(0, 3):
-        add(zz3)
-    with Locations(Plane.XY.offset(8)):
-        with PolarLocations(107.95 / 2, 6):
-            CounterBoreHole(6 / 2, 13 / 2, 4)
-
-show(p)
-print(f"\npart mass = {p.part.volume*densb:0.2f}")
+"""
+Too Tall Toby Party Pack 01-07 Flanged Hub
+"""
+
+from build123d import *
+from ocp_vscode import *
+
+densa = 7800 / 1e6  # carbon steel density g/mm^3
+densb = 2700 / 1e6  # aluminum alloy
+densc = 1020 / 1e6  # ABS
+
+with BuildPart() as p:
+    with BuildSketch() as s:
+        Circle(130 / 2)
+    extrude(amount=8)
+    with BuildSketch(Plane.XY.offset(8)) as s2:
+        Circle(84 / 2)
+    extrude(amount=25 - 8)
+    with BuildSketch(Plane.XY.offset(25)) as s3:
+        Circle(35 / 2)
+    extrude(amount=52 - 25)
+    with BuildSketch() as s4:
+        Circle(73 / 2)
+    extrude(amount=18, mode=Mode.SUBTRACT)
+    pln2 = p.part.faces().sort_by(Axis.Z)[5]
+    with BuildSketch(Plane.XY.offset(52)) as s5:
+        Circle(20 / 2)
+    extrude(amount=-52, mode=Mode.SUBTRACT)
+    fillet(
+        p.part.edges()
+        .filter_by(GeomType.CIRCLE)
+        .sort_by(Axis.Z)[2:-2]
+        .sort_by(SortBy.RADIUS)[1:],
+        3,
+    )
+    pln = Plane(pln2)
+    pln.origin = pln.origin + Vector(20 / 2, 0, 0)
+    pln = pln.rotated((0, 45, 0))
+    pln = pln.offset(-25 + 3 + 0.10)
+    with BuildSketch(pln) as s6:
+        Rectangle((73 - 35) / 2 * 1.414 + 5, 3)
+    zz = extrude(amount=15, taper=-20 / 2, mode=Mode.PRIVATE)
+    zz2 = split(zz, bisect_by=Plane.XY.offset(25), mode=Mode.PRIVATE)
+    zz3 = split(zz2, bisect_by=Plane.YZ.offset(35 / 2 - 1), mode=Mode.PRIVATE)
+    with PolarLocations(0, 3):
+        add(zz3)
+    with Locations(Plane.XY.offset(8)):
+        with PolarLocations(107.95 / 2, 6):
+            CounterBoreHole(6 / 2, 13 / 2, 4)
+
+show(p)
+
+
+got_mass = p.part.volume*densb
+want_mass = 372.99
+tolerance = 1
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.2f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
diff --git a/docs/assets/ttt/ttt-ppp0108.py b/docs/assets/ttt/ttt-ppp0108.py
index e79d1f95..60280c54 100644
--- a/docs/assets/ttt/ttt-ppp0108.py
+++ b/docs/assets/ttt/ttt-ppp0108.py
@@ -1,47 +1,54 @@
-"""
-Too Tall Toby Party Pack 01-08 Tie Plate
-"""
-
-from build123d import *
-from ocp_vscode import *
-
-densa = 7800 / 1e6  # carbon steel density g/mm^3
-densb = 2700 / 1e6  # aluminum alloy
-densc = 1020 / 1e6  # ABS
-
-with BuildPart() as p:
-    with BuildSketch() as s1:
-        Rectangle(188 / 2 - 33, 162, align=(Align.MIN, Align.CENTER))
-        with Locations((188 / 2 - 33, 0)):
-            SlotOverall(190, 33 * 2, rotation=90)
-        mirror(about=Plane.YZ)
-        with GridLocations(188 - 2 * 33, 190 - 2 * 33, 2, 2):
-            Circle(29 / 2, mode=Mode.SUBTRACT)
-        Circle(84 / 2, mode=Mode.SUBTRACT)
-    extrude(amount=16)
-
-    with BuildPart() as p2:
-        with BuildSketch(Plane.XZ) as s2:
-            with BuildLine() as l1:
-                l1 = Polyline(
-                    (222 / 2 + 14 - 40 - 40, 0),
-                    (222 / 2 + 14 - 40, -35 + 16),
-                    (222 / 2 + 14, -35 + 16),
-                    (222 / 2 + 14, -35 + 16 + 30),
-                    (222 / 2 + 14 - 40 - 40, -35 + 16 + 30),
-                    close=True,
-                )
-            make_face()
-            with Locations((222 / 2, -35 + 16 + 14)):
-                Circle(11 / 2, mode=Mode.SUBTRACT)
-        extrude(amount=20 / 2, both=True)
-        with BuildSketch() as s3:
-            with Locations(l1 @ 0):
-                Rectangle(40 + 40, 8, align=(Align.MIN, Align.CENTER))
-                with Locations((40, 0)):
-                    Rectangle(40, 20, align=(Align.MIN, Align.CENTER))
-        extrude(amount=30, both=True, mode=Mode.INTERSECT)
-        mirror(about=Plane.YZ)
-
-show(p)
-print(f"\npart mass = {p.part.volume*densa:0.2f}")
+"""
+Too Tall Toby Party Pack 01-08 Tie Plate
+"""
+
+from build123d import *
+from ocp_vscode import *
+
+densa = 7800 / 1e6  # carbon steel density g/mm^3
+densb = 2700 / 1e6  # aluminum alloy
+densc = 1020 / 1e6  # ABS
+
+with BuildPart() as p:
+    with BuildSketch() as s1:
+        Rectangle(188 / 2 - 33, 162, align=(Align.MIN, Align.CENTER))
+        with Locations((188 / 2 - 33, 0)):
+            SlotOverall(190, 33 * 2, rotation=90)
+        mirror(about=Plane.YZ)
+        with GridLocations(188 - 2 * 33, 190 - 2 * 33, 2, 2):
+            Circle(29 / 2, mode=Mode.SUBTRACT)
+        Circle(84 / 2, mode=Mode.SUBTRACT)
+    extrude(amount=16)
+
+    with BuildPart() as p2:
+        with BuildSketch(Plane.XZ) as s2:
+            with BuildLine() as l1:
+                l1 = Polyline(
+                    (222 / 2 + 14 - 40 - 40, 0),
+                    (222 / 2 + 14 - 40, -35 + 16),
+                    (222 / 2 + 14, -35 + 16),
+                    (222 / 2 + 14, -35 + 16 + 30),
+                    (222 / 2 + 14 - 40 - 40, -35 + 16 + 30),
+                    close=True,
+                )
+            make_face()
+            with Locations((222 / 2, -35 + 16 + 14)):
+                Circle(11 / 2, mode=Mode.SUBTRACT)
+        extrude(amount=20 / 2, both=True)
+        with BuildSketch() as s3:
+            with Locations(l1 @ 0):
+                Rectangle(40 + 40, 8, align=(Align.MIN, Align.CENTER))
+                with Locations((40, 0)):
+                    Rectangle(40, 20, align=(Align.MIN, Align.CENTER))
+        extrude(amount=30, both=True, mode=Mode.INTERSECT)
+        mirror(about=Plane.YZ)
+
+show(p)
+
+
+got_mass = p.part.volume*densa
+want_mass = 3387.06
+tolerance = 1
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.2f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
diff --git a/docs/assets/ttt/ttt-ppp0109.py b/docs/assets/ttt/ttt-ppp0109.py
index 34268465..b00b0bc2 100644
--- a/docs/assets/ttt/ttt-ppp0109.py
+++ b/docs/assets/ttt/ttt-ppp0109.py
@@ -1,56 +1,62 @@
-"""
-Too Tall Toby Party Pack 01-09 Corner Tie
-"""
-
-from math import sqrt
-from build123d import *
-from ocp_vscode import *
-
-densa = 7800 / 1e6  # carbon steel density g/mm^3
-densb = 2700 / 1e6  # aluminum alloy
-densc = 1020 / 1e6  # ABS
-
-with BuildPart() as ppp109:
-    with BuildSketch() as one:
-        Rectangle(69, 75, align=(Align.MAX, Align.CENTER))
-        fillet(one.vertices().group_by(Axis.X)[0], 17)
-    extrude(amount=13)
-    centers = [
-        arc.arc_center
-        for arc in ppp109.edges().filter_by(GeomType.CIRCLE).group_by(Axis.Z)[-1]
-    ]
-    with Locations(*centers):
-        CounterBoreHole(radius=8 / 2, counter_bore_radius=15 / 2, counter_bore_depth=4)
-
-    with BuildSketch(Plane.YZ) as two:
-        with Locations((0, 45)):
-            Circle(15)
-        with BuildLine() as bl:
-            c = Line((75 / 2, 0), (75 / 2, 60), mode=Mode.PRIVATE)
-            u = two.edge().find_tangent(75 / 2 + 90)[0]  # where is the slope 75/2?
-            l1 = IntersectingLine(
-                two.edge().position_at(u), -two.edge().tangent_at(u), other=c
-            )
-            Line(l1 @ 0, (0, 45))
-            Polyline((0, 0), c @ 0, l1 @ 1)
-            mirror(about=Plane.YZ)
-        make_face()
-        with Locations((0, 45)):
-            Circle(12 / 2, mode=Mode.SUBTRACT)
-    extrude(amount=-13)
-
-    with BuildSketch(Plane((0, 0, 0), x_dir=(1, 0, 0), z_dir=(1, 0, 1))) as three:
-        Rectangle(45 * 2 / sqrt(2) - 37.5, 75, align=(Align.MIN, Align.CENTER))
-        with Locations(three.edges().sort_by(Axis.X)[-1].center()):
-            Circle(37.5)
-            Circle(33 / 2, mode=Mode.SUBTRACT)
-        split(bisect_by=Plane.YZ)
-    extrude(amount=6)
-    f = ppp109.faces().filter_by(Axis((0, 0, 0), (-1, 0, 1)))[0]
-    # extrude(f, until=Until.NEXT) # throws a warning
-    extrude(f, amount=10)
-    fillet(ppp109.edge(Select.NEW), 16)
-
-
-show(ppp109)
-print(f"\npart mass = {ppp109.part.volume*densb:0.2f}")
+"""
+Too Tall Toby Party Pack 01-09 Corner Tie
+"""
+
+from math import sqrt
+from build123d import *
+from ocp_vscode import *
+
+densa = 7800 / 1e6  # carbon steel density g/mm^3
+densb = 2700 / 1e6  # aluminum alloy
+densc = 1020 / 1e6  # ABS
+
+with BuildPart() as ppp109:
+    with BuildSketch() as one:
+        Rectangle(69, 75, align=(Align.MAX, Align.CENTER))
+        fillet(one.vertices().group_by(Axis.X)[0], 17)
+    extrude(amount=13)
+    centers = [
+        arc.arc_center
+        for arc in ppp109.edges().filter_by(GeomType.CIRCLE).group_by(Axis.Z)[-1]
+    ]
+    with Locations(*centers):
+        CounterBoreHole(radius=8 / 2, counter_bore_radius=15 / 2, counter_bore_depth=4)
+
+    with BuildSketch(Plane.YZ) as two:
+        with Locations((0, 45)):
+            Circle(15)
+        with BuildLine() as bl:
+            c = Line((75 / 2, 0), (75 / 2, 60), mode=Mode.PRIVATE)
+            u = two.edge().find_tangent(75 / 2 + 90)[0]  # where is the slope 75/2?
+            l1 = IntersectingLine(
+                two.edge().position_at(u), -two.edge().tangent_at(u), other=c
+            )
+            Line(l1 @ 0, (0, 45))
+            Polyline((0, 0), c @ 0, l1 @ 1)
+            mirror(about=Plane.YZ)
+        make_face()
+        with Locations((0, 45)):
+            Circle(12 / 2, mode=Mode.SUBTRACT)
+    extrude(amount=-13)
+
+    with BuildSketch(Plane((0, 0, 0), x_dir=(1, 0, 0), z_dir=(1, 0, 1))) as three:
+        Rectangle(45 * 2 / sqrt(2) - 37.5, 75, align=(Align.MIN, Align.CENTER))
+        with Locations(three.edges().sort_by(Axis.X)[-1].center()):
+            Circle(37.5)
+            Circle(33 / 2, mode=Mode.SUBTRACT)
+        split(bisect_by=Plane.YZ)
+    extrude(amount=6)
+    f = ppp109.faces().filter_by(Axis((0, 0, 0), (-1, 0, 1)))[0]
+    # extrude(f, until=Until.NEXT) # throws a warning
+    extrude(f, amount=10)
+    fillet(ppp109.edge(Select.NEW), 16)
+
+
+show(ppp109)
+
+got_mass = ppp109.part.volume*densb
+want_mass = 307.23
+tolerance = 1
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.2f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
diff --git a/docs/assets/ttt/ttt-ppp0110.py b/docs/assets/ttt/ttt-ppp0110.py
index f62c56fc..9b3458fd 100644
--- a/docs/assets/ttt/ttt-ppp0110.py
+++ b/docs/assets/ttt/ttt-ppp0110.py
@@ -1,52 +1,59 @@
-"""
-Too Tall Toby Party Pack 01-10 Light Cap
-"""
-
-from build123d import *
-from ocp_vscode import *
-
-densa = 7800 / 1e6  # carbon steel density g/mm^3
-densb = 2700 / 1e6  # aluminum alloy
-densc = 1020 / 1e6  # ABS
-
-with BuildPart() as p:
-    with BuildSketch(Plane.YZ.rotated((90, 0, 0))) as s:
-        with BuildLine() as l:
-            n2 = JernArc((0, 46), (1, 0), 40, -90)
-            n3 = Line(n2 @ 1, n2 @ 0)
-        make_face()
-
-        with BuildLine() as l2:
-            m1 = Line((0, 0), (42, 0))
-            m2 = Line((0, 0.01), (42, 0.01))
-            m3 = Line(m1 @ 0, m2 @ 0)
-            m4 = Line(m1 @ 1, m2 @ 1)
-        make_face()
-        make_hull()
-    extrude(amount=100 / 2)
-    revolve(s.sketch, axis=Axis.Y.reverse(), revolution_arc=-90)
-    mirror(about=Plane(p.part.faces().sort_by(Axis.X)[-1]))
-    mirror(about=Plane.XY)
-
-with BuildPart() as p2:
-    add(p.part)
-    offset(amount=-8)
-
-with BuildPart() as pzzz:
-    add(p2.part)
-    split(bisect_by=Plane.XZ.offset(46 - 16), keep=Keep.BOTTOM)
-    fillet(pzzz.part.faces().filter_by(Axis.Y).sort_by(Axis.Y)[0].edges(), 12)
-
-with BuildPart() as p3:
-    with BuildSketch(Plane.XZ) as s2:
-        add(p.part.faces().sort_by(Axis.Y)[-1])
-        offset(amount=-8)
-    loft([p2.part.faces().sort_by(Axis.Y)[-5], s2.sketch.faces()[0]])
-
-with BuildPart() as ppp0110:
-    add(p.part)
-    add(pzzz.part, mode=Mode.SUBTRACT)
-    add(p3.part, mode=Mode.SUBTRACT)
-
-show(ppp0110)
-print(f"\npart mass = {ppp0110.part.volume*densc:0.2f}")
+"""
+Too Tall Toby Party Pack 01-10 Light Cap
+"""
+
+from math import sqrt, asin, pi
+from build123d import *
+from ocp_vscode import *
+
+densa = 7800 / 1e6  # carbon steel density g/mm^3
+densb = 2700 / 1e6  # aluminum alloy
+densc = 1020 / 1e6  # ABS
+
+# The smaller cross-section is defined as having R40, height 46,
+# and base width 84, so clearly it's not entirely a half-circle or
+# similar; the base's extreme points need to connect via tangents
+# to the R40 arc centered 6mm above the baseline.
+#
+# Compute the angle of the tangent line (working with the
+# left/negativeX side, given symmetry) by observing the tangent
+# point (T), the circle's center (O), and the baseline's edge (P)
+# form a right triangle, so:
+
+OT=40
+OP=sqrt((-84/2)**2+(-6)**2)
+TP=sqrt(OP**2-40**2)
+OPT_degrees = asin(OT/OP) * 180/pi
+# Correct for the fact that OP isn't horizontal.
+OP_to_X_axis_degrees = asin(6/OP) * 180/pi
+left_tangent_degrees = OPT_degrees + OP_to_X_axis_degrees
+left_tangent_length = TP
+with BuildPart() as outer:
+    with BuildSketch(Plane.XZ) as sk:
+        with BuildLine():
+            l1 = PolarLine(start=(-84/2, 0), length=left_tangent_length, angle=left_tangent_degrees)
+            l2 = TangentArc(l1@1, (0, 46), tangent=l1%1)
+            l3 = offset(amount=-8, side=Side.RIGHT, closed=False, mode=Mode.ADD)
+            l4 = Line(l1@0, l3@1)
+            l5 = Line(l3@0, l2@1)
+            l6 = Line(l3@0, (0, 46-16))
+            l7 = IntersectingLine(start=l6@1, direction=(-1,0), other=l3)
+        make_face()
+    revolve(axis=Axis.Z)
+sk = sk.sketch & Plane.XZ*Rectangle(1000, 1000, align=[Align.CENTER, Align.MIN])
+positive_Z = Box(100, 100, 100, align=[Align.CENTER, Align.MIN, Align.MIN])
+p = outer.part & positive_Z
+cross_section = sk + mirror(sk, about=Plane.YZ)
+p += extrude(cross_section, amount=50)
+p += mirror(p, about=Plane.XZ.offset(50))
+p += fillet(p.edges().filter_by(GeomType.LINE).filter_by(Axis.Y).group_by(Axis.Z)[-1], radius=8)
+ppp0110 = p
+
+got_mass = ppp0110.volume*densc
+want_mass = 211.30
+tolerance = 1
+delta = abs(got_mass - want_mass)
+print(f"Mass: {got_mass:0.1f} g")
+assert delta < tolerance, f'{got_mass=}, {want_mass=}, {delta=}, {tolerance=}'
+
+show(ppp0110)
diff --git a/pyproject.toml b/pyproject.toml
index 167ed019..4fc9a766 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -61,13 +61,14 @@ ocp_vscode = [
 
 # development dependencies
 development = [
-    "wheel",
+    "black",
+    "mypy",
+    "pylint",
     "pytest",
     "pytest-cov",
     "pytest-xdist",
-    "pylint",
-    "mypy",
-    "black",
+    "sympy",
+    "wheel",
 ]
 
 # typing stubs for the OCP CAD kernel
diff --git a/tests/test_examples.py b/tests/test_examples.py
index e342f0d1..5db4bf9e 100644
--- a/tests/test_examples.py
+++ b/tests/test_examples.py
@@ -18,6 +18,7 @@
 
 
 _examples_dir = Path(os.path.abspath(os.path.dirname(__file__))).parent / "examples"
+_ttt_dir = Path(os.path.abspath(os.path.dirname(__file__))).parent / "docs/assets/ttt"
 
 _MOCK_OCP_VSCODE_CONTENTS = """
 from pathlib import Path
@@ -72,8 +73,7 @@ def assert_example_does_not_raise(self):
 class TestExamples(unittest.TestCase):
     """Tests build123d examples."""
 
-
-for example in sorted(_examples_dir.iterdir()):
+for example in sorted(list(_examples_dir.iterdir()) + list(_ttt_dir.iterdir())):
     if example.name.startswith("_") or not example.name.endswith(".py"):
         continue
     setattr(