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Posted by ESC on April 04, 2005

In Reply to: RULE OF THUMB posted by lewis on April 04, 2005

: : : Does anyone know the word which means an equation which isn't scientifically proven but is known through knowledge? i.e like rule of thumb.
: : : Thanks for your help

: : Are you talking about what is known a priori (vs. a posteriori)?

: isn't 'rule of thumb' a rather poor example? from what I have heard the rule of thumb comes from the old legal principle that it was acceptable to beat your wife with a stick providing that it did not have a diameter larger that your thumb. a 'rule of thumb' is thus a simple principle (usually relating to measurement) easily understood and applied.

: 'rough approximation' is the expression I would use for a quick calculation that has a fairly well-known application - eg. "pi" being 22/7 might fit that although the mnemonic of the letter numbers in "how I wish I could calculate pi" is pretty handy for 3.141592.

: 'rules of thumb' arise in particular industries and I can't think of any examples from the real world, but if somebody says - "oh, it's 3 times the height in bags of gympsum and add 20%" you may have spotted one.

: L

RULE OF THUMB - "There are two good choices here. Brewmasters of old often tested the temperature of a batch of beer by dipping a thumb in the brew, their long experience telling them how well the beer was brewing. One theory has it that our expression for a rough, guesswork estimate derives from this practice. More likely it stems from the ancient use of the last joint of the thumb as a measuring device for roughly one inch." From the Encyclopedia of Word and Phrase Origins by Robert Hendrickson (Facts on File, New York, 1997).

A second reference also lists these two theories and adds a couple of details. The lower part of the thumb is roughly one inch long in the average adult male. And what the brewmaster was checking was the temperature of the beer, a practice that was "neither so accurate nor so hygienic as a thermometer check." From the Morris Dictionary of Word and Phrase Origins by William and Mary Morris (HarperCollins, New York, 1977, 1988).