Instrumental drift is continuous incremental change over time in indication, due to changes in metrological properties of a measuring instrument.
Instrumental drift is the gradual change over time in the indication provided by an instrument. It can be in either direction and can change direction over time.
Drift will affect the trueness of results if the true calibration parameters have changed between the time the instrument was calibrated and the time test samples are analysed. The extent to which an indication drifts therefore determines the required frequency of recalibration of the instrument. In analytical chemistry, a ‘drift correction standard’ with a known quantity value can be measured regularly to monitor the state of calibration of an instrument and determine whether adjustment to the configuration of the instrument or recalibration is required.
REF: Terminology in Analytica Measurement Introduction to VIM 3
