Without complex scientific knowledge. Without a laboratory to work on. Without money to pay the lab or someone to calibrate it for you. Hate reading scientific books or even simple scientific articles. Well, you can do thermometer calibration at home without those complexities.
There is one item at home that has two forms. The water. It is 100 C when boiling and 0 C when frozen. All you need to do is place the thermometer probe in boiling water or ice cubes. Record the actual reading. Then the adjustment works like this. Example. In boiling water, if the reading is 98 C and the thermometer has adjustment screw, turn the screw so it reads two degrees higher. If it has no any, then you have to add two points for every reading you make. If you are working with a digital thermometer, there must be a way to adjust it. Look for its manual.
This method only works if the application temperature range is close enough to water boiling or freezing point. If roasting requires 250 Centigrade. The 100 and 250 values are two far apart. Cannot be for body thermometer because the scaling is narrow. Infrared thermometers read surface temperature. It gonna give value of water pot wall instead of water. Even if the intention is measuring the wall temperature, the water acts as interference, giving out erratic reading.
Boiling point changes with altitude. You have to have a reference chart before proceeding. The change might not be much but it is worth considering. Water purity also affects boiling point. It is better to use distilled.
Marvin is the lead chocolate maker of Ben and Lyn Chocolate Inc. Has strong background in food research and development. Occasionally conducts training and lectures. Lecturer of Cocoa Foundation of the Philippines. Do coaching and consultancy services on his free time.