We have a set of Hanna "PHep" PH meters, that I've inherited from my predecessor. They are an arse. Plain and simple. For some insane reason, it's always been "the way" that the kids calibrate the things, with the screwdrivers. This has led to some being marked "f", and some "g" - presumably "fooked" and "good" or similar. Now, when I come to use them, they're uncalibratable - the heads on the polythene cermet pots are shredded, due to kids. Some just go insane - I was trying to calibrate some for A-level, and in PH4 buffer they'd refuse to go low enough, while in PH10 I'd get readings flickering between 4.0 and 13.5. They're expensive, they're mostly knackered, and the students calibrating them is to my mind insane..can anyone think of any reason this may be necessary? Also, what do you all use? I'd be happier if the meters were made with decent trimmers with brass pots, but I suppose that's cost. If I could solder well, I'd refurbish the damn things..