XPost: alt.usage.english   
   From: hr.usenet@email.de   
      
   On Thu, 19 Sep 2024, 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.   
      
   ... the English-speaking world with the exception of Ireland, Canada,   
   Australia, New Zealand, and South Africa and some others.   
      
   I think the term “United Kingdom and USA” would have been shorter and   
   slightly more accurate.   
      
   > 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.   
      
   And easier to remember than 1.609344. But when will you need such precision?   
   For instance, when you drive on German roads outside villages, you must   
   reduce your speed to 31.0685 mph whereas the rough rule 1 mi = 1.6 km would   
   have allowed you 31.2500 mph.   
      
   I like much more those thumb rules that actually allow you to estimate orders   
   of magnitude, e.g.:   
      
   1 year ≅ π · 10⁷ sec ≅ 31415926.54 sec   
      
   or   
      
   1 year ≅ √10 · 10⁷ sec ≅ 31622776.60 sec   
      
   or, only for those wanting more precision, the arithmetic mean of the two   
   which has three leading digits correct.   
      
   --   
   Helmut Richter   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)