That above accuracy of the 1PPS output is measured against a "reference" time:, ie. rubidium/cesium disciplined by GPS, etc.
It does not mean you could accumulate the -2.5ns diffs against a "reference time" and it will then make 8.46us/hour, afaik.
No, the way they present it, their PPS error must be accumulating. The histogram is the distribution of 21,567 period measurements of the PPS pulses. The article says it was over six hours, so those are sequential period measurements.
Adding up all those measurements would give a sum 21,567 x (-2.350 ns) = 50.68 us short of 21,567 seconds.
Assuming their master clock was perfect, the average frequency of their LEA-6T PPS would be 1.000 000 002 35 Hz, or 2350 ppt off.
Assuming Texaspyro's 5071 was perfect, the average frequency of his F9P came out to 0.999 999 999 999 834 Hz, or 0.17 ppt off.
Both tests were done over a period of several hours, maybe more for Tex's (I can't tell from the figures).
I ask because many of the GPSDO projects are using something like the NEO-6M to discipline an oscillator using the PPS long term average. If that doesn't converge to 1 Hz, then the oscillators won't converge on 10 MHz.
So, if a NEO-6M PPS is averaged over several hours, does it converge on 1 Hz?
Tim