Calibration Adjustment

Calibration adjustment is the corrective action taken when as-found calibration data shows an instrument is out of tolerance or when its readings need improvement. Adjustments can be as simple as zeroing an instrument or as complex as a multi-point linearization. Common adjustment actions include setting zero offset, adjusting span or gain, replacing worn components (like caliper jaws or micrometer anvils), and updating digital correction coefficients in smart instruments.

The key principle of calibration adjustment is that as-found data must always be recorded before any adjustment is made. This preserves the record of how the instrument was actually performing in service. After adjustment, as-left data is recorded to document the instrument's new condition. Some instruments are designated as "calibrate only — do not adjust," meaning their readings are documented but no adjustments are made; correction factors may be applied to measurements instead.

In calibration management, adjustment decisions involve balancing several factors. Not every out-of-tolerance instrument can or should be adjusted — some may need repair or replacement. The cost of adjustment versus replacement, the availability of adjustment procedures and reference standards, and the risk of future instability after adjustment all factor into the decision. Some organizations limit who can perform adjustments, requiring additional training or authorization beyond what is needed for basic calibration. All adjustments must be documented, including what was changed and the before/after readings.