This video shows how to zero-beat the WWV signal as a tool to adjust the frequency reference of an old frequency counter. It demonstrates the concept of zero-beat'ing a test signal against the WWV carrier. Since the WWV carrier is likely more accurate than any other frequency reference that most hobbiests and hams have in their labs, this is a useful technique. It can be used to check or adjust the 10MHz reference in the counter, if it has one, or can be used to very precisely set the output frequency of a signal generator which can then be used as a test signal for the frequency counter.
Similar techniques can be used to adjust the frequency accuracy of a ham radio's reference. Several years ago, I wrote up a procedure that I put on my website. If can be found here: