Process variable

The current temperature is the process variable, while the desired temperature is known as the set-point (SP).

[1] Measurement of process variables is essential in control systems to controlling a process.

The value of the process variable is continuously monitored so that control may be exerted.

Four commonly measured variables that affect chemical and physical processes are: pressure, temperature, level and flow.

[citation needed] but there are in fact a large number of measurement quantities which for international purposes use the International System of Units (SI) The SP-PV error is used to exert control on a process so that the value of PV equals the value of the SP.