You can spend a small fortune buying Ph testers, Most of them are made in ????? China or another Far Eastern country.
On the Wedliny USA Forum there, has been and still is, a great deal of discussion about them.
The probes seem to be the bug-bear, expensive and not lasting very long.
An advertised German made model was actually made in China as well. It didn’t reflect in the retail price though.
Some members prefer to stick with the “correct range” ph strips.
Not 100% correct but it gives you an indication of what is happening.
My 2 cents worth.