I had a weird thing happened the other day, my Starrett caliper (American-made) decided to change its zero point. It was on the 12 o'clock position and now it's in the 3 o'clock position .My first thought was that was some debris and between the jaws. I cleaned them so many times I think I was starting to removing metal! They had been right on and working perfectly before this happened. I have a magnet on my toolbox and when I'm not using them I stick it to the magnet. I've been doing it for a long time with no ill effects, just thought I'd run it by you guys and see if it's ever happened to you.