Calibration is the comparison of a measurement device (an unknown) against an equal or better standard. A standard in a measurement is considered the reference; it is the one in the comparison taken to be the more correct of the two. One calibrates to find out how far the unknown is from the standard.
Why do I need to calibrate my equipment?
As time goes on, the base accuracy (a known value) of your tester can change.This can be influenced by many factors ranging from a sudden surge of electricity to actually damage to the meter’s internal operation through accidental knocks. When this occurs, the meter’s accuracy ‘drifts’ from its normal state,potentially meaning that your equipment is inaccurate.
Calibration is the process of checking that your instruments are operating at their correct level of accuracy. If there is a slight imbalance, a calibration technician will fix it and restore the meter to its correct working order. Similarly if there are errors caused by faulty internal parts, calibration can help to discover these issues and repairs can be made.
In short, you need to calibrate your equipment as it could be inaccurate, leading to dangerous installations or incorrectly installed equipment.