Laboratory controllers are designed to monitor and/or control variables in laboratory or scientific experimentation, testing, or sample preparation. They are often used to control temperature, but may control other variables. Product specifications for laboratory controls include: number of inputs, number of outputs, input types, output types, and number of zones. The number of inputs is the total number of signals sent to the laboratory controller. The number of outputs is the sum of all outputs used to control, compensate or correct the laboratory process. Input types for a laboratory control include: direct current (DC) voltage, current loops, analog signals from resistors or potentiometers, frequency inputs, and switch or relay inputs. Output types include analog voltage, current loops, switch or relay outputs, and pulses or frequencies. Some laboratory controllers can also send inputs or receive outputs in serial, parallel, Ethernet or other digital formats which indicate a process variable. Others use an industrial fieldbus protocol such as CANbus, SERCOS, or PROFIBUS® (PROFIBUS International).