Equipment
How hot (or cold) is it?
There are many times in the cooking process where you want to know the exact temperature of something, from checking the temperature of meat to see if it's done, to monitoring the temperature of cooking oil for frying, to making sure the sugar you're melting gets to the hard crack stage. There are a variety of different thermometer types, both analog and digital.
Probe thermometers are very useful for monitoring the the temperature of an oven or smoker and can be programmed to alert you when the meat you're cooking reaches a specified temperature. Traditional glass thermometers are generally very accurate, and are good for monitoring the temperature of liquids. An infrared thermometer can give you the temperature of any surface instantaneously, but is useless for checking internal temperatures.