If your TM Hostas starts acting crazy and will not calibrate. Check to see if the Hall effect sensor magnet has fallen off.
The magnet sits on two small plastic pins. On internet photos, some of the pins look like they were melted to make the magnet stay in place but then some looked like mine with no melted blob of plastic.
I used a DAP super glue suitable for plastics to put it back in place. Greased the ball too.
I also found a very loose ground screw in the base and fixed that.
Several good yotube videos on how to dissemble these bases.
