Question edited for clarity.
Question moved from Cars and Trucks.
You just buy another one when they start to malfunction. I used to buy this type of thermometer 10 at a time. In catering they lasted 6 months. The advertising page doesn't say about Calibration, but ours had to be done and recorded once a month. We filled a glass with ice and added water. Let it sit for 10 minutes, stir and put the thermometer in and leave it until is settles. Press and hold the button at the end. Try removing your battery and wait 10 minutes before inserting it again.
Features/Benefits
Supco
https://www.supco.com > supco_live > products > ST09
ST09. ST09--DIGITAL THERMOMETER. Digital pocket thermometer with protective sheath and convenient pocket clip. Temperature range -40°F to 392°F (-40°C to 200 ...
Supco ST09 Digital Pocket Thermometer, 2-1/2-Inch Stem
Amazon.ca
https://www.amazon.ca > Supco-ST09-Digital-Pocket-...
Supco ST09 Digital Pocket Thermometer, 2-1/2" Stem, -40 to 392 Degree F ... Digital pocket thermometer with protective sheath and convenient pocket clip.
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Supco ST09 Digital Pocket Thermometer, 2-1/2" Stem
testequipmentdepot.com
https://www.testequipmentdepot.com > supco-st09-dig...
Digital Pocket Thermometer, 2-1/2" Stem Length, -40° F to 392° F · Accuracy: +/- 2° F (-14° F to 212° F, -10° C to 100° C) · Temperature range: -40° F to 392° F ...
US$19.17
Supco -40/392 C/F Digital Pocket Thermometer - ST09
The Master Group
https://www.master.ca > professional > supco-40-392-...
Supco® ST09 Digital Pocket Thermometer, -40 to 392 deg F, +/- 2 deg F Accuracy, 2-1/2 in L Stem, 1.5 V LR44 Battery.