diff --git a/Project#01/README.md b/Project#01/README.md
index 946ff71..b6a1d47 100644
--- a/Project#01/README.md
+++ b/Project#01/README.md
@@ -97,7 +97,7 @@ Diagonal:
 
 <img src="./figures/inertia-diag.png" width="750">
 
-Off-diagonal:
+Off-diagonal (add a negative sign):
 
 <img src="./figures/inertia-off-diag.png" width="600">
 
diff --git a/Project#01/hints/step7-solution.md b/Project#01/hints/step7-solution.md
index 4f9515a..babca70 100644
--- a/Project#01/hints/step7-solution.md
+++ b/Project#01/hints/step7-solution.md
@@ -94,9 +94,9 @@ int main()
     I(0,0) += mi * (mol.geom[i][1]*mol.geom[i][1] + mol.geom[i][2]*mol.geom[i][2]);
     I(1,1) += mi * (mol.geom[i][0]*mol.geom[i][0] + mol.geom[i][2]*mol.geom[i][2]);
     I(2,2) += mi * (mol.geom[i][0]*mol.geom[i][0] + mol.geom[i][1]*mol.geom[i][1]);
-    I(0,1) += mi * mol.geom[i][0]*mol.geom[i][1];
-    I(0,2) += mi * mol.geom[i][0]*mol.geom[i][2];
-    I(1,2) += mi * mol.geom[i][1]*mol.geom[i][2];
+    I(0,1) -= mi * mol.geom[i][0]*mol.geom[i][1];
+    I(0,2) -= mi * mol.geom[i][0]*mol.geom[i][2];
+    I(1,2) -= mi * mol.geom[i][1]*mol.geom[i][2];
   }
 
   I(1,0) = I(0,1);
@@ -215,9 +215,9 @@ Torsional angles:
 Molecular center of mass:   0.64494926   0.00000000   2.31663792
 
 Moment of inertia tensor (amu bohr^2):
-    156.154091561645       0.000000000000      52.855584120568
+    156.154091561645       0.000000000000     -52.855584120568
       0.000000000000     199.371126996236       0.000000000000
-     52.855584120568       0.000000000000      54.459548882464
+    -52.855584120568       0.000000000000      54.459548882464
 
 Principal moments of inertia (amu * bohr^2):
       31.964078  178.649562  199.371127
diff --git a/Project#01/hints/step8-solution.md b/Project#01/hints/step8-solution.md
index 32a9ea8..f85cabf 100644
--- a/Project#01/hints/step8-solution.md
+++ b/Project#01/hints/step8-solution.md
@@ -94,9 +94,9 @@ int main()
     I(0,0) += mi * (mol.geom[i][1]*mol.geom[i][1] + mol.geom[i][2]*mol.geom[i][2]);
     I(1,1) += mi * (mol.geom[i][0]*mol.geom[i][0] + mol.geom[i][2]*mol.geom[i][2]);
     I(2,2) += mi * (mol.geom[i][0]*mol.geom[i][0] + mol.geom[i][1]*mol.geom[i][1]);
-    I(0,1) += mi * mol.geom[i][0]*mol.geom[i][1];
-    I(0,2) += mi * mol.geom[i][0]*mol.geom[i][2];
-    I(1,2) += mi * mol.geom[i][1]*mol.geom[i][2];
+    I(0,1) -= mi * mol.geom[i][0]*mol.geom[i][1];
+    I(0,2) -= mi * mol.geom[i][0]*mol.geom[i][2];
+    I(1,2) -= mi * mol.geom[i][1]*mol.geom[i][2];
   }
  
   I(1,0) = I(0,1);
@@ -229,9 +229,9 @@ Torsional angles:
 Molecular center of mass:   0.64494926   0.00000000   2.31663792
 
 Moment of inertia tensor (amu bohr^2):
-    156.154091561645       0.000000000000      52.855584120568
+    156.154091561645       0.000000000000     -52.855584120568
       0.000000000000     199.371126996236       0.000000000000
-     52.855584120568       0.000000000000      54.459548882464
+    -52.855584120568       0.000000000000      54.459548882464
 
 Principal moments of inertia (amu * bohr^2):
       31.964078  178.649562  199.371127
diff --git a/Project#01/output/acetaldehyde_out.txt b/Project#01/output/acetaldehyde_out.txt
index c5916c0..8ef02f9 100644
--- a/Project#01/output/acetaldehyde_out.txt
+++ b/Project#01/output/acetaldehyde_out.txt
@@ -77,9 +77,9 @@ Moment of inertia tensor:
 
            1           2           3
 
-    1 156.1540916   0.0000000  52.8555841
+    1 156.1540916   0.0000000 -52.8555841
     2   0.0000000 199.3711270   0.0000000
-    3  52.8555841   0.0000000  54.4595489
+    3 -52.8555841   0.0000000  54.4595489
 
 Principal moments of inertia (amu * bohr^2):
 	  31.964078  178.649562  199.371127