I did a simple test run. driving the 1PPS input with a Tbolt.. over 2 hours the reported PRS case temperature varied 0.8 C. The TT time tag varied 60 ns (75 ns / degree). The FC frequency control word varied the frequency by 0.231 ppt (0.300 ppt / degree). All my high res counters are tide up doing other things, so I could not measure the actual freq. It looks like the PRS10 time tag processor / interpolator is rather crappy. I need to feed it the 1PPS from a 5071A to eliminate any temperature effects on the Tbolt. I did modify the message polling code to read the case temperature every second. That increased the time needed to get all the data values from the PRS10 to 35 seconds... a 10 second increase, You can only get around 5 values per second from the PRS10 and there are around 50 values it can report. If three of those 5 values per second are TT, FC, and AD10 that leaves room for getting 2 of those 50 values per second. ----------- > Have you done a least-square fit to determine the sensitivity?