Long time ago, Microchip had that AN592 to show how a PIC16C54 can measure up to 50MHz frequencies, which was indeed very impressive.

About 6 years ago this Instructable by user WilkoL did a High resolution frequency counter based on the Reciprocal method, so he can measure frequencies of the Hz region at 1 sec gate with 7 digits precision!

https://www.instructables.com/High-R...uency-Counter/

Later he made another one with variable gate https://www.instructables.com/Freque...ble-Gate-Time/

The above were not PIC based of course.

But as my freq. counter is not behaving lately I thought I may try to make one based on the above.

Then there is also this module https://www.aliexpress.com/item/1005...-specification at a price you can't beat...!

What is your prefered route if you did something similar?

Ioannis