thermometer pieces of crap

ive always used a spirit thermometer to measure my mash temperatures but when i dropped it once it got a bubble so i bought a digital. now the buuble in the old one is gone and is ready my cuurent mash at 71oC which is too high and the new digital one says its at 61oC way too low.

so i test them both in a glass of icy water:
spirit = 1oC (sounds quite close)
digital = -2oC (seems unlikely)

in boiling water:
spirit = 101oC (sounds right)
digit = 97.5oC (clearly wrong)

Then i put them both back in my mash and both read exactly 66.7oC which is perfect. i dont know whether to trust them and if my mash isgoing to be ruined. why would they be acting like this?

It is probably because you have hot and cool spots throughout the mash. You have to stir it a couple time and let the temperature stabilize. I use 2 thermometers and at first I get 2 way different readings. But after I stir up the mash, and move the thermometers around, they begin reading the same.