This is a modification of the original firmware for the "Frequency Counter with a PIC and minimum hardware" created by Wolfgang "Wolf" Büscher, DL4YHF.

Derivatives of Wolf's design are sold on Ebay and other sides in kit form, usually adding a crystal test circuit but otherwise using Wolf's exact design and firmware for the counter part (Wolf is aware of these "clones" but doesn't mind as long as "those kits are offered for a fair price").

This is for those PIC 16F628 kits.