Re: OT: Converting miles/km

On Thu, 19 Sep 2024 23:12:52 +0000, Christian Weisgerber wrote:

I'm sorry, I don't know where to post this.  I'm crossposting to
alt.usage.english, because statute miles as a unit mostly afflict
the English-speaking world.
>
So you want to convert between miles and kilometers.  The conversion
factor is... uh...  A 40-year-old calculator book provides a useful
tip:  Unless you're designing a space probe, you can use ln(5).
>
WHAT?
>
Yes, the natural logrithm of 5 approximates the conversion factor
between miles and kilometers; specifically one mile is about ln(5)
kilometers.  It's accurate to four digits.
>
If nothing else, it's faster to type on a calculator.
>
I think that's hysterical.

Hey, that's closer than the golden ratio.
I only know log(5) = about 1.6 because my graduate adviser
suggested I learn log(2) = 0.7, log(3) = 1.1, log(7) = 2, and
log(20) = 3.  It was handy for what I was doing.
--
Jerry Friedman