How do I check the temperature inside my refrigerator accurately?

Ideal refrigerator temperatures are 4 °C or 5 °C for the fridge and -18 °C for the freezer compartment. 

The best way to check the temperature inside your appliance is with an accurate thermometer. Place the thermometer inside a cup of water and put it inside the fridge compartment. 

To check freezer temperatures, do the same with the thermometer inside alcohol or cooking oil (because water would freeze).