Create FFT Diagram

Hello everyone!
I have found the solution for the variable "time" and I can now use this interesting FFT diagram.
The results were strangely enough always the same graph with a spike at aprox. 23,4 Hz with Amplitude of aprox. 5 µV.
Doesn't matter which patient data I was using, or which channel I was selecting; always the same graph came out.
Anyone could explain this?