On Sunday, February 28, 2021 at 4:27:15 PM UTC-5, Tinkerer wrote:
I have a Heathkit ET-3100 electronic design experimenter that has a very
basic sine/ square wave function generator. Controls all analog and no
scale really. Output is from 200 Hz - 2 Khz on "low" and 2 Khz to 20
Khz on "high". Exact frequency depends on where the pot is adjusted.
How can I calibrate this to be more precise, preferably in a simple way?

Frequency counter. They have cheap Chinese kits on ebay that should give you readings close enough to what that generator would be used for.