# Thread: Metrology and true value

1. Hi, Why when we measure something and get several values from diferent measures to the same thing we have to take the arithmetic mean as the true value? I am starting in physics lab. and really need this info. Thank you for your help.

2.

3. Its just the most likely of all the measurements, but more likely than not the true measurement falls either side. Its more scientific to take the standard deviation and calculate a random error, Then give a figure like 678+/-0.5

4. Thank you. Yes thats right, but lets say that i only have 6 values from from 6 measures (e.g 6-8-9-6-7-8, true value=7.333...) of the same thing, why we take the arithmetic mean as the true value? does it have something to do with Gaussian distribution?

5. Yes, indeed. The mean will be a the peak with 66% of the measurements lying under the standard deviation of the curve.

6. Thank you very much, i was thinking something like that but wasn`t sure.

7. NP. I would worry about it, I'm sure it will all be explained to you are you will be given the formulas to calculate error.

Do you know the difference between mean, median and mode? its surprising how few people do.

8. Originally Posted by hotchickwithalmostnoclotheson
Do you know the difference between mean, median and mode? its surprising how few people do
.

I know.

Oh, and BTW.....did you do capability study for the measurement system. Something along the lines of a Gauge R&R or at least some iso-plot?

9. Originally Posted by Manwhotriedtoeatatubofcartdo'rquickly
Originally Posted by hotchickwithalmostnoclotheson
Do you know the difference between mean, median and mode? its surprising how few people do
.

I know.

Oh, and BTW.....did you do capability study for the measurement system. Something along the lines of a Gauge R&R or at least some iso-plot?
No Im just a Physics student not a quantity surveyor.

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