[time-nuts] Correcting measured PPS values with receiver sawtooth correction values

[Mark Sims]

I am adding the ability to Lady Heather to apply receiver sawtooth correction values to measured PPS values... this requires having a receiver that outputs sawtooth values as the main input device and connecting a TICC/counter measuring the receiver PPS output as an auxiliary input device.

There are six different ways of calculating the corrected PPS value:  add/subtract the previous/current/next sawtooth value from the measured PPS value.   The combination that works properly depends upon the receiver and counter.   It is easy to find the correct combination by trying each one and seeing which one produces the "best" results ("best" being determined by which one had the lowest corrected PPS span, average, sdev, variance, etc).

For all the receivers that I have tested there is only one combination that jumps out as being the correct one.   However, for the new Ublox F9P, there are two combinations that produce virtually identical measurements and statistics (add current sawtooth or subtract previous sawtooth).  Any ideas on how to determine which combination is the "correct" one?