Calibration worksheet: error, TUR and a decision at every point

How the calculation works

1. 01Error at each point is the device reading minus the reference reading. Tolerance and expanded uncertainty are each stated as a fixed part plus a percentage of the reference reading, which is the form specifications and laboratory scopes are written in.
2. 02The decision uses the guard band rule of ILAC-G8 and JCGM 106: with a guard band w = g × U, a result inside the tolerance less w passes, one inside the tolerance but beyond that is a conditional pass, one just outside the tolerance but within w is a conditional fail, and anything further out fails. With g = 0 it is simple acceptance.
3. 03The test uncertainty ratio at each point is the tolerance span divided by twice the expanded uncertainty at 95 %, as in ANSI/NCSL Z540.3, with the stated coverage factor converted to k = 2 first.
4. 04As found and as left are decided separately and the overall result is the worst point. An as-found error outside the tolerance itself is flagged, because everything the device measured since its last good calibration may then need an impact assessment.

Limitations

• It is a worksheet, not a certificate. It cannot know that the reference was traceable, that the uncertainty is complete, or that anyone has reviewed the result, and the record it produces says so.
• The uncertainty is an input. Build it with the uncertainty budget calculator from the calibration itself, not from the reference's datasheet.
• The decision rule must be the one agreed with the customer or required by your quality system. The guard band default is ILAC-G8's, not a statement that it is right for your case.
• Nothing is stored. Closing the page loses the worksheet, so copy the record or download the CSV.

Frequently asked questions

What is the difference between as found and as left?

As found is what the device read before any adjustment, and as left is what it read after. Recording both matters: the as-found values show whether the device was in tolerance while it was in use, which decides whether earlier measurements need an impact assessment, and the as-left values show what you are handing back.

How do I decide pass or fail with measurement uncertainty?

With a decision rule agreed in advance. Under ILAC-G8's default a guard band equal to the expanded uncertainty is taken off each tolerance limit, so a result must be inside the tolerance by at least U to pass outright. Results between that and the tolerance limit are conditional passes, because the true value could be outside tolerance.

What does conditional pass mean?

The measured value is inside the tolerance but not by enough to rule out, given the uncertainty, that the true value lies outside it. It is reported as conditional so the customer can decide, instead of being rounded up to a pass.

Why use a percentage of reading as well as a fixed amount?

Because that is how most specifications and calibration laboratory scopes are written, for example ±(0.1 °C + 0.05 % of reading). The worksheet applies each term at each point, so the tolerance and uncertainty both change across the range.

How many calibration points should I enter?

Enough to cover the range the device is used over, including the ends. Five points across the span is a common minimum. The worksheet takes as many rows as you give it.