xkcd #3138: Dimensional Lumber Tape Measure

Title text:

A person with two watches is never sure what time it is, especially if I got them one of the watches.

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Source: https://xkcd.com/3138/

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A person with two watches is never sure what time it is, especially if I got them one of the watches.
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[–] 119 points 1 year ago* (last edited 1 year ago) (4 children)

Interestingly enough, this concept was used in pattern making for casting machine parts back before modern machining and parts manufacturing.

They were colloquially called shrink rulers, and looked like a standard ruler, but were actually longer to account for the shrinkage of the material being cast.

For example, say you're casting a part from iron, which shrinks 1% as it cools, which amounts to 1/8 inch per foot.

An iron shrink rule would look standard, but actually measure a foot as 1 foot 1/8 inches to account for the shrinkage (this is an example and not meant to be actually accurate).

Source: am historian that interviewed pattern makers that used shrink rulers in their work.

Edit: spelling

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  • I need to get a shrink tape ruler like this. I own a skoolie (used school bus converted to a motorhome) which is 35' 4" long from bumper-to-bumper. A lot of campsites have rules where RVs can't be longer than 35'. My thought was to get a tape measure with feet just slightly longer than normal and use it to make my bus appear to be shorter than 35'.

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