Step 1: Construction
The loop at the end is for coupling to my oscillator. The current on the line is measured by placing a diode against the line and measuring the voltage across it.
Step 2: The Measurement
The distance between two successive dips (or peaks) on the meter is taken to be half a wavelength.
In my case this distance was about 25 cm and so the wavelength is around 50 cm, a frequency of around 600 MHz.
The movie shows one such maximum deflection on the meter.
So, as I had promised, here is the frequency of my UHF oscillator.