The Leica outside world interface is an ASCII NMEA like based system, which is of course the sensible way to talk to a receiver. Leica, unlike Ashtech, don’t allow you to skip the checksum.
NMEA_Add_Checksum monitors the clipboard for anything that looks like a NMEA string without a checksum (starts with a $ and ends with a *) if it finds this it adds the checksum to the information in the clipboard.
The system monitors the clipboard every second.
So the normal way to use the system is enter the command you want in notepad, copy the text to tthe clip board and then switch to hyperterminal and paste the clipboard. By this time the checksum will have automatically have been added.