RE: Tolerance in text

["Jonathan West" <jwest -at- mvps -dot- org>]

>
> 25 ± 0.1 means 24.9 to 25.1 is acceptable. From everything I was taught,
> the measuring tool used should be accurate to one more decimal place than
> the tolerance. So, a micrometer that measures in ten thousandths is good
> for measuring any part requiring tolerances in the thousandths. I'd have
> to delve back into other text books for the exact allowances.
>
> So, in the preceding example 25.11 is too large and 24.89 is too small.

No. In that example, (assuming the measuring device has a measurement
uncertainty of 0.01) the acceptable range of *measured* values is 24.91 to
25.09. Only within that range can you be sure that the measured value
combined with the maximum measurement uncertainty means that the *actual*
value is within the required range of 24.9 to 25.1.



Regards
Jonathan West

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