Q: How do I "calibrate" my incubator thermometer?
A: It's definitely best to calibrate any new thermometer you are using for your incubator. You need to make sure your incubator thermometer is reading correctly, since even one degree of difference may cause serious problems with your hatch!
It's fairly easy to calibrate with crushed ice: your thermometer should read 32 degrees in a mixture of crushed ice and a little water. If it reads, say, 30 degrees, then you can either adjust the thermometer until it is correct (if the style of the thermometer permits adjustment), or else you will at least know your thermometer reads 2 degrees too cool, so you can adjust your thinking---and your incubator---accordingly.