If you connect the Thunderbolt EFC voltage up to the oscillator, Lady Heather's oscillator autotune (&a) command does a good job of characterizing the EFC slope/gain (Hz/volt) characteristics of a 10 MHz oscillator. It will step the EFC voltage up and down a few millivolts around the 10 MHz point and calculate the oscillator EFC gain. --------------------- > I love using a Thunderbolt/NTBW50AA for making frequency measurements this way. I remove the OCXO, and insert the 10MHz from the DUT. Then disable disciplining so the DAC voltage doesn't try to chase the open loop oscillator