xkcd #3023: The Maritime Approximation
xkcd #3023: The Maritime Approximation
It works because a nautical mile is based on a degree of latitude, and the Earth (e) is a circle.
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Obligatory repeat of the fact that the ratio between miles and kilometres is ln(5), correct to less than 0.01% (yes, that's a percent of a percent).
The golden ratio or Fibonacci numbers are used more often for the same trick but they're off by, at best, very slightly worse than 0.5%.
Fibonacci numbers are easier than ln(5) to calculate on the spot tho
You're not wrong. The ln(5) trick is for when you have a scientific calculator but it doesn't have the conversion built in.
correct to less than %%
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