# How many Uncertainty Measurements for Micrometers and Calipers?

#### garyf2017

##### Involved In Discussions
Hi, I've done some uncertainty measurement for caliper and micrometer but do I need to do uncertainty for every points for example 0-1 inches- I need to do uncertainy for each points? 0 - .5 - .75 etc...

or just the maximum?

TIA.

#### Richard Wilde

##### Registered
Hi there,

Uncertainty of measurement is the error you get when you repeat the measurement and is applied to all the readings.

So, if your measuring at .5 then the uncertainty to measurement will be the same if you are measuring to .75 and across the board.

Does this make sense?

Thanks.

#### dwperron

Trusted Information Resource
Hi there,

Uncertainty of measurement is the error you get when you repeat the measurement and is applied to all the readings.

So, if your measuring at .5 then the uncertainty to measurement will be the same if you are measuring to .75 and across the board.

Does this make sense?

Thanks.

I'm afraid you are dishing out some bad information here.

Repeatability, not measurement uncertainty, is the error when you repeat measurements. It is just one of the components that must be taken into account when you are calculating measurement uncertainty.

Linearity of the tool is another factor in calculating the measurement uncertainty, which is why the uncertainty at 0.5 and 0.75 may not be the same.

In answer to the original poster, you can report the worst case measurement uncertainty for the range of the tool, or you can report the measurement uncertainty of the actual measurement you are making (which is usually smaller).

#### Charles Wathen

##### Involved - Posts
You should have Type A and Type B. Below is what would be used for a micrometer.
Type A would be repeated measurements - micrometer repeatability using 10 measurements.
Type B would include:
Gage block specifications
Coefficient of Thermal Expansion of Gage Block
Micrometer Resolution