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From: Hibou <vpaereru-unmonitored@yahoo.com.invalid>
Newsgroups: sci.lang,alt.usage.english
Subject: Re: OT: Converting miles/km
Date: Fri, 20 Sep 2024 06:22:28 +0100
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Le 20/09/2024 à 00:12, Christian Weisgerber a écrit :
>
> 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.

Afflict? Sometimes I wonder how many more times I'm going to hear 
Germans criticising how we do things.

> 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.

I'm afraid I don't see the problem. Just assign 1.609344 to a memory 
cell. That's what I do. A shortened version is fine for mental 
arithmetic - better than ln(5) - and if one has forgotten 1.6... but has 
a calculator, what's wrong with tapping 2.54 x 12 x 5,280 / 100,000?

Simples!