Calories (thermoc.)
A thermochemical calorie, often abbreviated as cal_th, is a unit of energy that is primarily used in the field of chemistry. It is defined as the amount of energy required to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere, precisely defined as 4.184 joules.
Calories (20°C)
A Calorie (20°C) is sometimes referred to as a small calorie or gram calorie. It is a unit of energy defined as the amount of heat required to raise the temperature of one gram of water by one degree Celsius from 19.5°C to 20.5°C.