In the old days mechanical watches were calibrated in seconds by using the tick sound converted to a narrow pulse to sample the phase of a tuning fork reference. (as long as the tick sound was accurately detected for peak to a pulse much smaller than the wavelength of the reference and is equal in f or a subharmonic of some crystal reference.
The phase error was then plotted on mini-thermal printer.
Any slope to the phase error would indicate a frequency error and the watch repair guy could tune it in seconds.
I have used the same principle in Doppler tracking of scientific rockets and 4Mbps PLL clock sync designs, many times.
Use a trimmed 10MHz crystal oscillator (XO) trimmed to any better reference (VLF, WWVB, GPS, OCXO etc) ,
If you dont own a frequency counter, you can buy one or make an analog measurement do the same quickly. Essentially using any known reference frequency can be use dto measure an unknown clock and measured quickly depending with ppm resolution using a DMM and an analog or digital mixer.
e.g.
Convert XO sine or squarewave to sawtooth.
Then using selectable counter divider PLL simple breadboard, choose the reference clock to match the DUT clock or harmonic to match, such that the harmonic frequency difference is zero.
e.g. if you had a 2MHz XO being tested use a std calibrated 10MHz XO and either divide by 5 or use square to sawtooth and S&H as a phase detector to measure phase asa voltage with DMM, then null slope on trimcap on DUT clock so you get a steady intermediate voltage.
e.g. if you had 1 Hz clock, use an XOR gate with RC delay on one side to make a narrow edge detector and frequency doubler as well as sample pulse for a 1MHz sawtooth.
Now you get 1 PPM resolution full scale every tick of the clock on your DMM.
e.g. if you are measuring unknown clock frequencies, then using a dial-a frequency synthesizer with BCD thumbwheel presets to BCD counters from 1MHz clock say and compare the beat frequency for null.