Calibrations can be absolute or relative. Absolute calibrations are not biased by the calibration reference and would, therefore, be more reproducible. However, absolute calibrations can be more complex to determine. The bias in relative calibrations would be consistent if all the devices in the system are calibrated against the same calibration reference. Calibrations may also be performed relative to other devices without reference to an absolute standard. Relative calibrations are generally simpler to perform than absolute calibrations.