Rule of thumb
From Wikipedia, the free encyclopedia
A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination. Compare this to heuristic, a similar concept used in mathematical discourse, or in computer science, particularly in algorithm design. See also mnemonic.
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[edit] Origin of the term
The term "rule of thumb" or similar stands in many languages and cultures for "quickly understood, easily used, practical method".
[edit] Domestic violence/discipline
It is often claimed that the term originally referred to the maximum thickness of a stick with which it was permissible for a man to beat his wife. This explanation for the origin of the term was popularized in the opening of the 1999 movie The Boondock Saints.
Linguist Michael Quinion, citing the research of Sharon Fenick, notes that there are some examples of a related usage historically — most notably with regard to a supposed pronouncement by a British judge, Sir Francis Buller. However, it is questionable whether Buller ever made such a pronouncement and there is even less evidence that he phrased it as a "rule of thumb"; the rumoured statement was so unpopular that it caused him to be lambasted as "Judge Thumb" in a satirical James Gillray cartoon. According to Quinion, the term "Rule of Thumb" was first documented in English in 1692, long before Buller's reported pronouncement. The first known usage of the phrase "rule of thumb" in direct reference to domestic violence was in 1976, in the book Battered Wives by Del Martin.
[edit] Use as a physical measurement
The measurement of an inch is derived from the distance between the base of the thumbnail and the first joint. This is a plausible origin as the thumb is often used for rough measurement by carpenters, seamstresses, artists and many others.
[edit] The Russian Tzar
The Russian Tzar Alexander II has been suggested as the creator of this term. In an apocryphal story he is said to have drawn the route of a railroad from St. Petersburg to Moscow, accidentally tracing his thumb. The engineers, nervous about disobeying his orders, laid the tracks with an unnecessary curve according to the line drawn.
[edit] Used to determine wind direction
A technique for approximating the general direction of the wind involves wetting the thumb then raising it in the air.
[edit] Used for plate settings at the Royal table
A technique for setting a row of plates an equal distance from the table edge. Plate setters, setting plates for an English Royal banquet, place the plate against the tip of the thumb while holding the arch of the thumb and first finger against the table edge.
[edit] Examples of usage
Financial - Rule of 72 A rule of thumb for exponential growth at a constant rate. An approximation of the "doubling time" formula used in population growth, which says divide 70 by the percent growth rate. In terms of money, it is easier to use 72 (rather than 70) because it is easily divisible by 12 (the number of months in a year). Therefore, divide 72 by the percent interest rate to determine the approximate amount of time to double your money in an investment. For example, at 10% interest, your money will double in approximately 7.2 years (72/10=7.2).
Tailors' Rule of Thumb A simple approximation that was used by tailors to determine the wrist, neck, and waist circumferences of a person through one single measurement of the circumference of that person's thumb. The rule states, typically, that twice the circumference of a person's thumb is the circumference of their wrist, twice the circumference of the wrist is the circumference of the neck, and twice around the neck is the person's waist. For example, if the circumference of the thumb is 4 inches, then the wrist circumference is 8 inches, the neck is 16 and the waist is 32. An interesting consequence of this is that — for those to whom the rule applies — this simple method can be used to determine if pants will fit: the pants are wrapped around the neck, and if the two ends barely touch, then they will fit. Any overlap or lack thereof corresponds to the pants being too loose or tight, respectively.
