How to connect Raspberry Pi and mechanical frequency counter?

Question

Iron

What is the best way to connect a Raspberry Pi to a mechanical frequency counter?
The frequency meter is a comb of rods of different lengths. When exposed to a comb with different frequencies, some rods enter into resonance and vibrate more strongly. It is their fluctuations that I need to trace.

Answer 1

What is the interface of this device?

Answer 2

It’s easier to take an accelerometer, write history and study its spectrum, in terms of sensitivity it will be no worse than a mechanical frequency meter.

Answer 3

The device does not have an interface, you need to fence something of your own. That's why I'm asking which is better.
The accelerometer is not exactly what you need - you want to write both the main and additional harmonics at the same time.