> Why is 1/3 so critical to represent but not 1/10?
TLDR reason: Every second number is divisible by 2. Every third number is divisible by 3.
So if you want to divide something (like donuts or cans of beer, or the length of a wood plank) by N, it's far more likely that N will have a factor of 2 or 3 than it will not have a factor of 3, but be divisible by 10. Which is to say, you are far more likely to need tick marks spaced by 1/2 and 1/3 than tick marks spaced by 1/10. Which is to say that a 12-inch ruler is preferable to a 10 cm ruler, Q.E.D.
That's why they sell donuts by the dozen, and beer in 6-packs. And why the US officially (and Canada and the UK unofficially) still use English units for everyday measurements. Its just more practical.
TLDR reason: Every second number is divisible by 2. Every third number is divisible by 3.
So if you want to divide something (like donuts or cans of beer, or the length of a wood plank) by N, it's far more likely that N will have a factor of 2 or 3 than it will not have a factor of 3, but be divisible by 10. Which is to say, you are far more likely to need tick marks spaced by 1/2 and 1/3 than tick marks spaced by 1/10. Which is to say that a 12-inch ruler is preferable to a 10 cm ruler, Q.E.D.
That's why they sell donuts by the dozen, and beer in 6-packs. And why the US officially (and Canada and the UK unofficially) still use English units for everyday measurements. Its just more practical.