Calorimeter is used for measuring the heat of chemical reactions or physical changes as well as heat capacity. Constant volume oxygen bomb calorimeters are most often used when it comes to determining the calorific values of liquid and solid samples. These calorimeters work by igniting the sample in an atmosphere of pure oxygen. The heat of combustion is transferred to the calorimeter and can be determined by its temperature increase. Bomb calorimeters are usually calibrated with a standard of a known heat of combustion. Modern devices are fully automated and require little user input.