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.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3138/
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
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'.
It shrinks? Like a frightened turtle!
That’s what happens when things cool down… It is the cold, that why it looks small 😳
Neat!