This is a quartz crystal tester my father built 50+ years ago (maybe from a QST article), though I added a Ramsey frequency counter to its output. I also changed the tube to a 6GM6 to get it to work up to around 40MHz. It will not do the kind of crystals like those from digital watches, as these are very low frequencies, less than about 900KHz.

It will run the crystal under test at its fundamental frequency, so crystals made to operate on the third overtone will oscillate on its fundamental, approximately ⅓ the marked third overtone frequency. The meter will show the "activity" of the crystal. And the frequency counter will display this fundamental. My father used a few differing crystal socket styles, and I added a couple more, to make crystal testing easier.