Every sensor is designed to work over a specified range.
The design ranges are usually fixed, and if exceeded, result in permanent damage to or destruction of a sensor. It is customary to use transducing elements over only the part of their range where they provide predictable performance and often enhanced linearity. When making a measurement it is necessary to start at a known datum, and it is often convenient to adjust the output of the instrument to zero at the datum. It, therefore, is a value ascribed to some defined point in the measured range. The signal level may vary from its set zero value when the sensor works.