A question on Pendulum experiment

[jmnk]

I just wonder what it means for a non-driven case.

Not so much… ¯\_(ツ)_/¯

But I do not understand why there is clump of data points at ~0.83Hz and another at ~0.8357Hz.  What is so special about those particular frequencies?

Uneducated guess: perhaps some “quantization” in the numerical autocorrelation algorithm? I need to check that…

Thank you.  If you have a moment to check that - that would be great. I'm trying to read the the .phyphox source to see what the logic is - but it will be few days before I fully understand.