Measuring instrument

A device that determines the magnitude or value of a physical quantity through sensing, comparison, or another measurement method.

Transducer: A device that converts energy or a physical quantity into another form, often an electrical signal. Many instruments use transducers to turn an otherwise inaccessible quantity into a readable signal.
Measurement: The process of experimentally obtaining one or more values that can reasonably be attributed to a quantity. An instrument is a tool within the wider process of assigning values to quantities.
Thermometer: An instrument that measures temperature. Thermometers turn thermal behavior into a value through expansion, electrical response, or radiation.
Measurement standard: A defined realization of a quantity used as a reference for measurement. Unlike an ordinary instrument, a standard serves as the reference against which instruments are calibrated.
Calibration: The comparison of an instrument's readings with reference standards to establish measurement relationships. Calibration connects an instrument's indications to known quantities and reveals systematic error.
Accuracy and precision: Accuracy is closeness to a true or reference value; precision is agreement among repeated measurements. These distinct properties describe whether an instrument is correct and whether its readings are consistent.
Barometer: An instrument that measures atmospheric pressure. Barometers infer pressure from effects such as liquid-column height or deformation of a sealed chamber.
Sensor: A device that detects a physical input and responds with a signal or observable change. A sensor may detect a quantity without independently presenting a complete measurement result.
Measurement uncertainty: A quantified range expressing doubt about the value assigned to a measured quantity. An instrument's reading is incomplete without the uncertainty associated with its measurement.
Resolution (measurement): The smallest change in a measured quantity that an instrument can distinguish. Resolution sets how finely an instrument can display or detect changes.

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