Heathkit SG-8 Signal Generator

[Notimetolooz]

About that 2420 counter, since it is capable of high accuracy there are a few things you should understand about frequency counters.
The oven crystal oscillator is very stable, however there is an adjustment, a calibration, that is critical so that the display is as accurate as it can be.
The oscillator is capable of staying on frequency within better than 1 ppm (one part per million) that is 0.0001 %, much better than any voltage, current or resistance meter measurement. You need that much accuracy if all 8 digits of the display will mean anything.
However if the crystal oscillation is only calibrated to an accuracy of, say, 0.1% then the display will be off that much. So the calibration needs to be checked from time to time against a frequency source of even more accuracy.
One way is by using super accurate frequency radio broadcasts from stations like WWV and WWVH. More modern methods use GPS managed frequency standards.