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From: jerry.friedman99@gmail.com (jerryfriedman)
Newsgroups: sci.lang,alt.usage.english
Subject: Re: OT: Converting miles/km
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Date: Fri, 20 Sep 2024 13:50:20 +0000
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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