using the code of post 18 on a CYD if I input a frequency of 36.8 HZ
I get a displayed frequency of 37Hz
a input of 123Hz gives PCNT 1152 and frequency 123
However, the PCNT module is good for measuring stable pulse inputs over long periods but I understand you are attempting to measure RPM signals for a mechanical switch
the technique of counting rising/falling edge interrupts of post 31 would probably be more suitable and using a smoothing technique on the results
e.g. inputting 123Hz gives output
2621 123 122
2622 122 122
2623 123 122
2624 123 122
2625 123 122
2626 123 122
2627 123 122
2628 123 122
2629 123 122
and inputting 36.8Hz gives
3843 36 36
3844 36 36
3845 36 36
3846 36 36
3847 36 36
3848 36 36
3849 36 36
will see if I can get a version working on the CYD