What are the units used for a thermometer?

Temperature is usually express in one of 4 units:

°C: Celsius (aka Centigrade) - most common

°F: Fahrenheit - in the USA and some other places

K: Kelvin - mostly for scientific and engineering calculations. Has the same intervals as Celsius but has a different starting point: 0 °C is 273.15 K. Note that unlike the other temperature units, the abbreviation for Kelvin does not use the ° "degree" symbol

°R: Rankine - used in engineering and sometimes science where Fahrenheit is the usual unit of temperature. Like Kelvin, it starts at 0° at the "absolute zero" of thermodynamics. 0 °F corresponds to 491.67 °R.