This brief video gives a simple walk through on measuring the resonant frequency of both parallel and series resonant circuits such as what is in the Multiwave Oscillator (MWO) or many other Tesla type systems. This can even be used to measure the simple resonant frequency of ignition coils or just about any kind of inductor.
This video walks you through doing all of this with nothing more than a small current transformer, which is simply a ferrite toroidal core with a few windings of magnet wire, an analog voltmeter, and a few wires with alligator clips. There are of course more sophisticated methods such as with Vector Network Analyzers and so forth but this low budget and low-tech method will give you the correct answer.
A Vril Lakhovsky MWO is used with the demo to show this simple method also with some comments by Eric Dollard toward the end as to another variation he recommends still using the same tools.
This is so simple that anyone can learn this method even if you have very little technical experience.
Part of the 2020 Energy Science & Technology Conference series (33 mins downloadable video).