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 at its two states. 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 and frozen water. 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.