Total posts : 45366
First make sure the counter locks on to the signal. If the frequency reading is steady it is OK, if it is bouncing around it is not locked.
The specs from the RS link state “initial accuracy 1 ppm” which doesn’t say much and is not usable to determine the accuracy. Usually modestly priced counters without crystal ovens are +/-10 ppm. or thereabouts. This translates to about +/-1kHz in the FM band which is adequate for part 15 stuff.
Let everything stabilize before trusting the readings with a 10 minute “warm up” usually being satisfactory. The reading should not be drifting appreciably where drifting would indicate something is not stable. And don’t connect the counter to the oscillator since this can pull the frequency. Connect it to the tx. output if it will lock on the signal.
Here I have a Phase Matrix counter with a crystal oven which is on all the time the unit is plugged in. I check it against WWV about once a year and it stays in spec. I also have a $100 el cheapo counter which, when compared to the PM unit, does drift but the drift from a cold start is usually less than 200 Hz at 10 MHz. Absolute accuracy after “warm up” is generally better than 10 Hz at 10 MHz at stable room temp but I periodically recalibrate it with the PM. This is good enough for general lab work and part15 and ham stuff.