Does anyone know off hand the specification for the checksum appended to messages over RS232 when enabled with CHK1 command?

I couldn't find anything in the manual about it. Looks like it adds two ASCII characters eg:

0005 C0M 23:32:46.82 00>5
0006 C1M 23:32:47.06 00>4

Anyone know what the deal is?

Looks like it's just the 8 bit sum of message characters converted to ASCII.