## Re: Tolerance in text

Subject: Re: Tolerance in text
From: Dick Margulis <margulisd -at- comcast -dot- net>
Date: Tue, 21 Feb 2006 08:57:28 -0500

Hi All,

I have a few questions about measure tolerances wrote in text.

Diederik,

Perhaps English is not your first language? I just want to point out, gently, that the correct word in that sentence is "written," not "wrote."

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Point 1:
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What is the best way to write a measure with tolerance - where both '+' and '-' are equal - in a text (or non-technical illustration)?

I normally write:
"Drill a hole with a diameter of 25 +/-0.2 mm."
My colleque writes:
"Drill a hole with a diameter of 25 ±0.2 mm."

I _obviously_ prefer the first one.
Because the '±'-sign means 'approximately' (the hole can be 24 mm or 26 mm) and not 'plus or minus' (the hole must be between 24.8 mm and 25.2 mm).

Where did you get that idea? The "±" sign means "plus or minus"; it does not mean "approximately." Your colleague is correct, except that there should be no space preceding the ± character. "+/-" is typewriter substitution for a typographic character not readily available on a typewriter keyboard. It has no place in typeset work of any kind.

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Point 2:
--------
What notation is correct or more, preferrable:
A. "Drill a hole with a diameter of 25 +/-0.2 mm."
"Drill a hole with a diameter of 25 mm +/-0.2 mm."

Drill a hole with a diameter of 25±0.2 mm.

Note that there is no space around the operator. This means 24.8 to 25.2 mm.

B. "Drill a hole with a diameter of 25 +0.2/0.5 mm."
"Drill a hole with a diameter of 25 +0.2 mm/0.5 mm."

This makes no sense. Do you mean a range of 25.02 to 25.05? In that case, write 25.35±0.15 mm.

Note: In drawings, you will often see a notation of an asymmetric tolerance. For example, a hole diameter might be indicated as 25 mm and then next to it are two stacked superscripts, "-0.0," and "+0.2," to emphasize to the machinist that there is no tolerance for the hole to bee too small, but it's okay for it to be a bit large. Rendering this in text you would need to convert it to 25.1±0.1 mm.

HTH,

Dick

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References:
Tolerance in text: From: Links, Diederik