The FA-2 manual doesn’t specify any accuracy, only “resolution” (10s: 0.00001Hz@10MHz). I wanted to figure what I would consider as the accuracy for the CH1 input at 10S gate time. I connected a coax from 10 MHz REF OUTPUT to CH1. Set GATE=10S and IMP=50 ohms. Ran for one hour reading the serial port. Plotted the error (Reading-10MHz). The stated resolution is 1e-5. In the one hour run, the error for seven of 350 readings was greater than the “resolution”. For whatever reason, when reading from serial, the resolution is 1e-9. The LCD display resolution is 1e-5. I’m showing the error of the serial read resolution on the plot. I don’t know why they spew out so many digits when they are meaningless. Anyway, for my purposes based on this data, for a 10S gate time on CH1, I’m going to round to 1e-4. That gives me a 12 digit counter that’s dead on for $130. I bought this on eBay from a US seller so I wouldn’t have to wait. I tweaked the Ref pot on this (and my two Rubidiums) the other day based on a GPSDO that I finally got from China. For years I’ve been using an HP5386A that I got from eBay. The internal reference is crap, so I got some eBay LPRO 101s for a good deal, and I only use the HP if I have a rubidium for a reference. I just turned on my scope to see how close the FA-2 ref is to my GPSDO. I’m too impatient to wait for the result; it’s been 20 minutes, and it hasn’t slipped a half cycle yet. That’s better than 5e-11. I’m very happy with this FA-2. No need to fire up a rubidium to make a pretty decent frequency measurement. Some day I’m going to open it up and match the CH2 to 50 ohms.