Calibration is adjusting, or realigning, an instrument to accurately indicate the measured variable, as compared with a traceable standard.

If an instrument has not been calibrated or has not been calibrated regularly you can never be certain that it is reading accurately. The reading is arbitrary.

Sigma Technical Services can calibrate the following types of instruments to ANSI/NCSL Z540.1-1999 (R2002), ISO/IEC 17025, EN 45001