Explanation of Rule of Thumb (10:1) - Tolerance Zone or Digits Number

Gabiddon said:

Hello,

Could You give me some explanation of rule of thumb (10:1).

1. Does "rule of thumb" apply to tolerance zone or tolerance number of digits (or maybe both).

For example dimension:
5.5 +/-0.25
a) tolerance zone: 0.5
b) number of digits: 0.01

Rule of thumb:
a) 0.05
b) 0.001

Which way is correct? Point a) or b) ?

2. Is there any difference (in case of measurement) when we analyse two dimensions:

A) 6 +/-1
B) 6 +/-1.0

Kind Regards
Tom

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Gabiddon said:

Hello,

Could You give me some explanation of rule of thumb (10:1).

1. Does "rule of thumb" apply to tolerance zone or tolerance number of digits (or maybe both).

For example dimension:
5.5 +/-0.25
a) tolerance zone: 0.5
b) number of digits: 0.01

Rule of thumb:
a) 0.05
b) 0.001

Which way is correct? Point a) or b) ?

Click to expand...

Gabiddon said:

2. Is there any difference (in case of measurement) when we analyse two dimensons:

A) 6 +/-1
B) 6 +/-1.0

Kind Regards
Tom

Click to expand...

Jim Wynne said:

Use the total tolerance, or "a" in your example.


In both cases the total tolerance is 2. The 10:1 "rule" says that your gage tolerance (combining resolution and uncertainty) should be 10% or less of the total tolerance band of the thing being measured. Sometimes the "rule" is interpreted to apply to gage resolution irrespective of uncertainty. In your example of a tolerance of ±1, (a total tolerance of 2) the gage should resolve to .2.

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