A related question is:  Do you use positive or negative numbers to set the 
antenna cable delay value?  Again, most GPS receiver documentation does not 
say.    I think that I've only seen it explicitly mentioned in the Trimble 
documentation and the Oscilloquartz Star-4 documentation.

Also there is the question of does the receiver time message come out before or 
after the 1PPS and what is the message offset time from the 1PPS?   Again, 
rarely documented by the receiver manufacturer.   Lady Heather can measure 
those (if the operating system clock is accurately set)  Heather uses the 
message time offset to adjust the displayed time or get the audible "tick 
clock" aligned to true time.  

Heather has a table of typical message offsets for the supported receivers, but 
measuring and setting the value for your receiver/computer/serial port can 
improve things.
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