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/
You don't even need a custom one. Readily available is the universal tape measure where the relationship is marked as 2.54 units, equals 1 inch.
It means that a 2 x 4 is actually 5.08 x 10.16, which leaves you with a margin for surfacing and sanding.
american lumber doesn't use standard imperial units. an "inch" isn't the standard you'd expect on a so-called "nominally" 2 inch by 4 inch board. just attempting to use metric without accounting for the extra wackiness added by lumber 'measurement' on top of standard imperial silliness, you'd end up with a bunch of errors.
tl;dr: a 2" x 4" board actually measures something like 3.81cm x 7.62cm.
I understand.
I was making a joke about secretly introducing a metric tape measure.
I realise that my sense of humour is not universal, like the use of SAE .. or Fahrenheit 😇