I finally got hands on some hardness testers (via Amazon USA) for knife making. Of course I had to test them right away and they’re great!

The set consists of six graded files with different hardnesses. What you do is scrape over your workpiece beginning with the lowest grade and working yourself upwards. The first file that leaves a mark on your steel tells you the achieved hardness in HRC. (Pictured above is my fishing knife, that I made 2015. It has a hardness of about 60 HRC!!!)