Traceability and Calibration

Calibration compares an instrument against a reference of known accuracy and records the result. It does not automatically adjust the instrument, and the distinction matters: calibration establishes what the instrument reads; adjustment changes it.

Traceability

A calibration is meaningful only if the reference is itself traceable through an unbroken chain of comparisons, each with stated uncertainty, to a national or international standard. A certificate without traceability establishes that two instruments agree with each other, which is not the same as either being correct.

What a calibration certificate should show

• The instrument identified uniquely, and its condition on receipt — as found results as well as as-left.
• The reference standards used and their traceability.
• The measured values at each calibration point, not merely a pass statement.
• The measurement uncertainty of the calibration.
• Environmental conditions where they affect the result.
• The date and the calibrating body's accreditation.

Why "as found" matters most

A certificate showing only the as-left condition conceals whether the instrument was out of tolerance before adjustment. If it was, everything measured with it since the previous calibration is in question, and that assessment can only be made if the as-found data exists.

A calibration sticker confirms a date. Only the certificate confirms what the instrument was actually doing.