Note: APRS 1.2.1 data is technically a comment.

The APRS 1.2.1 addendum notes that new values like flood stage, voltage,
radiation, and device type (F, V, X, and Z, respectively) are all part
of the comment field.  This was confusing the heck out of me.  Hopefully
this keeps other people from being confused, too.

Author: rhymeswithmogul

man/aprs-weather-submit.man

@@ -177,6 +177,7 @@ If you specify a value outside of this range, it will be reduced (that is, a rep
 (APRS 1.2)
 The water level above or below the flood stage or mean tide.
 You may report numbers from \-99.9 feet to 99.9 feet, with a resolution of 0.1 feet.
+Note that this data is technically part of the comment field and may not be parsed by all APRS decoders as weather data.
 .TP
 .BR \-g ", " \-\-gust =\fISPEED\fP
 The peak wind speed measured in the past five minutes.
@@ -225,17 +226,20 @@ If both \fB-t\fP and \fB-T\fP are specified, the last option specified will be r
 (APRS 1.2)
 The battery voltage.
 You may report voltages of up to 99.9 volts, with a resolution of one-tenth of a volt.
+Note that this data is technically part of the comment field and may not be parsed by all APRS decoders as weather data.
 .TP
 .BR \-X ", " \-\-radiation =\fINANOSIEVERTS\fP
 (APRS 1.2)
 The current level of nuclear radiation.
 You may report readings of up to 99,000,000,000 nanosieverts per hour, though the resolution of the value put into your report varies based on orders of magnitude.
 Consult the APRS 1.2 specification for full details.
+Note that this data is technically part of the comment field and may not be parsed by all APRS decoders as weather data.
 .TP
 .BR \-Z ", " \-\-device\-type =\fIDEVICE-TYPE\fP
 (APRS 1.2.1)
 Exactly two characters to identify the type of device sending this information.
 The device types are not defined in the APRS specification and are implementation-specific.
+Note that this data is technically part of the comment field and may not be parsed by all APRS decoders as weather data.
 .SH EXAMPLES
 .PP
 If you were operating the ARRL's (theoretical) weather station at their headquarters and wanted to submit a temperature of 68 degrees Fahrenheit, no rainfall, and a westerly wind at about five miles per hour, use this command:

src/aprs-wx.c

@@ -344,8 +344,8 @@ printAPRSPacket (APRSPacket* restrict const p, char* restrict const ret,
 		strcat(result, p->radiation);
 	}
 
-	/* F is required by APRS 1.2 if voltage is present  */
-	if (notNull(p->waterLevel) || notNull(p->voltage))
+	/* F is required by APRS 1.2.1 if voltage or device type are present  */
+	if (notNull(p->waterLevel) || notNull(p->voltage) || notNull(p->deviceType))
 	{
 		strcat(result, "F");
 		strcat(result, p->waterLevel);