Define "hysteresis" in the context of instrumentation.

Hysteresis refers to the phenomenon where there is a discrepancy in the measurement of a system that occurs under varying conditions, particularly when transitioning from an increasing state to a decreasing state. In instrumentation, this typically manifests as a difference in the readings of a measuring device, such as a pressure gauge or a temperature sensor, when the input conditions change direction. This difference arises because the internal mechanisms or characteristics of the measuring device may respond differently when the variable is increasing versus when it is decreasing, leading to two distinct readings for the same input value.

Understanding hysteresis is crucial for accurate measurements and control in various applications, as it can affect the precision and reliability of instrumentation data. It's essential for engineers and technicians to be aware of hysteresis to make informed decisions about device calibration, application suitability, and overall device selection.