Broadback writes
Can someone recommend a good min/max thermometer for my greenhouse
please? I purchased one with 2 indicators that looked like pencil lead
and a button to press to "zero" them. It was hopeless, the indicators
did not always zero and on doing so tended to bounce back up. The only
way to get it to work was subjecting to centrifugal force by wind
milling it with my arm.

See if you can slide the indicators down with a magnet.
--
Kay