Calibration instruments use electrical signals or physical quantities to calibrate sensors and meters. Devices that produce electrical signals can serve as precise meters for sensor calibration, or send output signals to other devices. Common calibration signals include AC voltage, DC voltage, AC current, and DC current. Calibration instruments that produce a pulse stream, pulse range, or frequency range are also available. Signal and waveform generators are designed to produce a sine wave, square wave, triangular wave, or other predefined waveform. Most manufacturers specify calibration instruments with a range of signal values that includes minimum and maximum amounts. Devices that produce physical quantities are often traceable to national to international standards from the National Institute of Standards and Technology (NIST), Physikalisch-Technische of Bundesanstalt (PTP), National Measurement Accreditation Services of the U.K. (NAMAS), or Bureau Nationale Metrologie of France (BNM).