Components of a Calibration Certificate

Accuracy/Error

The actual error of the instrument may then have been calculated and shown or a correction value is given. ('Correction' is the algebraic opposite of 'error' and by convention corrections are algebraically added to results.)

At some point however, it may be tiresome to correct large errors of an instrument and the instrument will need to be adjusted. It is critical to maintaining a valid history that calibration values are determined before adjustments are made, and then those same values are measured again after the adjustments.

These are sometimes listed on certificates as 'pre-cal' and 'post-cal' values or sometimes 'as found' and 'as left' values. However they are named, the use of these values can allow the continued determination of the drift to be maintained.

Of course, if an instrument becomes faulty and requires repair and re-adjustment, then 'pre-cal' values cannot be determined and the historical data becomes less useful.

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