# New to Gage Block Calibration Reports

#### dgriffith

##### Quite Involved in Discussions
In a cal report for gage blocks, a company indicated their uncertainties as described below.
Question: What does the L in +1L and +2L mean?

Measurement Uncertainty:
0.01 - 0.95 in. = ?(3 + 1L) uin.
1.00 - 4.00 in. = ?(3 + 2L) uin.

On longer lengths, it is only stated as:
5 inch = 11 uin
6 inch = 18 uin, and so on.

#### Jen Kirley

##### Quality and Auditing Expert
Leader
Admin
Hello,

As NIST describes in 3.3 of its document Uncertainty and Dimensional Calibrations (from Journal of Research of the National Institute of Standards and Technology), L involves the potential error due to thermal expansion. That is, the block's length as affected by temperature. The length can differ between actual use conditions and the conditions within a calibration laboratory. The amount of difference depends on things like material and how long the block is.

I hope this helps!

#### dgriffith

##### Quite Involved in Discussions
Yep. I've already accounted for environmental factors. Just didn't know what the L was, so now I know its additional length due to temps, etc.

So why the 2L? I guess I'm missing something in the terminology. The additional length is multiplied by two for longer blocks? It seems like the gaging face would grow (or shrink) uin per in/in. Why would it matter just because 1 inch was reached?

Last edited:

#### Jen Kirley

##### Quality and Auditing Expert
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NIST describes L as simply Length in 3.3 of its document Measurement Assurance for Gage Blocks; NBS Monograph 163; 1979

ΔL/L = αL ΔT

L is the length, ΔL is the change in length of the object, ΔT is the temperature change and αL is the coefficient of thermal expansion (CTE)

Because temperature-impacted length of gage blocks tends to lessen as they get longer, the figure L in a formula, representing length as a result of temperature's impact, does not change at a straight line. The figures you quoted would have seemed obvious if the thermal expansion coefficient was traceable in terms of 1L for 1 inch, 2L for 2 inch etc. But it's instead traceable on a curve. So the 1L or 2L etc. is meant to help to mathematically calculate temperature's actual "error" introduction to the gage block's length.

All, if I got this wrong please feel free to chime in. Hershal?

#### Hershal

##### Metrologist-Auditor
Trusted Information Resource
I think you did a good job Jennifer. Well done.

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Z

#### zancky

from my understanding

0.01 - 0.95 in. = ?(3 + 1L) uin.
1.00 - 4.00 in. = ?(3 + 2L) uin.

means
if You have a gauge block of nominal length 0.05 in. the uncertainty is ?(3 + 1*0.05) uin.

if the length is 1.20 the uncertainty is ?(3 + 2*1.2) uin.

i.e
1) they are fitting formula for range of length
2) the laboratory have more "trouble" in measuring parts over 1 inch

T
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