RULE OF THUMB

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.

Contents

Origin of the term

Use as a physical measurement

Distance approximation

Hours of Daylight Remaining

Used to determine wind direction

Used to measure the coldness of beer

Domestic violence/discipline

Used for plate settings at the Royal table

The Russian Tsar

Examples of usage

References

External links

See also

Origin of the term

This has been said to derive from the belief that English law allowed a man to beat his wife with a stick so long as it is was no thicker than his thumb. In 1782 Judge Sir Francis Buller is reported as having made this legal ruling. The following year James Gillray published a satirical cartoon attacking Buller and caricaturing him as 'Judge Thumb'. The cartoon shows Buller carrying two bundles of sticks and the caption reads "thumbsticks - for family correction: warranted lawful!"
It seems that Buller was hard done by. He was notoriously harsh in his punishments, but there's no evidence that he ever made the ruling that he is infamous for. Edward Foss, in his authoritative work The Judges of England, 1870, wrote that, despite a searching investigation, "no substantial evidence has been found that he ever expressed so ungallant an opinion".
It's certainly the case that, although British common law once held that it was legal for a man to chastise his wife in moderation (whatever that meant), the 'rule of thumb' has never been the law in England. Despite the phrase being in common use since the 17th century and appearing many thousands of times in print, there are no printed records that associate it with domestic violence until the 1970s. The false stories that assumed the wife-beating law to be true may have been influenced by Gillray's cartoon.
Even if people mistakenly believed that law to exist, there's no reason to connect the legal meaning with the phrase - which has been in circulation since at least 1692, when it appeared in print thus:
Sir W. Hope, Fencing-Master, 1692 - "What he doth, he doth by rule of Thumb, and not by Art."
That makes it clear that the origin refers to one of the numerous ways that thumbs have been used to estimate things - judging the alignment or distance of an object by holding the thumb in one's eye-line, the temperature of brews of beer, measurement using the estimated inch from the joint to the nail, etc. It isn't clear which of these is the precise origin and this joins the whole nine yards as a phrase that probably derives from some indetermined form of measurement.

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. This connection to anatomy is also present in other languages. For example, the Spanish word for inch is ''pulgada'', the Portuguese word is ''polegada'', derived from ''pulgar'' or ''polegar'', meaning "a thumb's length". Another example is the French phrase ''un pouce'' meaning both "a thumb" and "an inch". A sixteenth century instrument German instrument maker named Geor Hartmann (1489-1564), in his 1527 treatise on making astrolabes, instructs the reader to make the astrolabe plates "3 daumen" wide, and in this case the thumb would be the entire thumb as evidenced by his surviving astrolabes.

Distance approximation

The distance of a far-away object can be estimated by comparing the height of ones thumb at an arms distance to the perceptive height of a distant tree or building which height could be readily estimated. This method would be generally imprecise and the result would mainly be based on the experience of the person making the estimation.

Hours of Daylight Remaining

Hold your outstretched hand horizontal at arm's length with your palm facing you; for each hand width the sun is above the horizon, there is one remaining hour of sunlight.

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.

Used to measure the coldness of beer

In England, before the advent of thermometers, bar-tenders used to stick their thumbs in a beer to ensure its coldness. It is also said that it was standard practice at this time to stick one's thumb into the boiled wort to ensure that it wasn't too hot to accommodate the yeast.

Domestic violence/discipline

While 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.^[1] This claim has been completely debunked. The "Domestic Violence" 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, noted 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, that a man may legally beat his wife, provided that he used a stick no thicker than his thumb. 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.
In reality, British law since the 1700s and American laws predating the Revolution prohibited wife beating. ^[2] In his work on the Common Law, Sir William Blackstone plainly stated that common law prohibited violence against wives. ^[3] Various Historians and Legal Experts who research the "rule of thumb" myth promoted by feminists found that it was nothing but an urban legend. "It has often been claimed that wife-beating in nineteenth-century America was legal... Actually, though, several states passed statutes legally prohibiting wife-beating; and at least one statute even predates the American Revolution. The Massachusetts Bay Colony prohibited wife-beating as early as 1655. The edict states: "No man shall strike his wife nor any woman her husband on penalty of such fine not exceeding ten pounds for one offense, or such corporal punishment as the County shall determine." ^[4]

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.

The Russian Tsar

The Russian Tsar Nicholas I 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.

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 (the actual number is 69.3147181 from the natural logarithm of 2, if the percent growth is much much less than 1%). In terms of money, it is frequently easier to use 72 (rather than 70) because it works better in the 4%-10% range where interest rates often lie. 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 8% interest, your money will double in approximately 9 years (72/8 = 9).
'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 trousers will fit: the trousers are wrapped around the neck, and if the two ends barely touch, then they will fit. Any overlap or lack thereof corresponds to the trousers being too loose or tight, respectively.
'Marine Navigation'
A ship's captain should navigate to keep the ship more than a thumb's width from the shore, as shown on the nautical chart being used. Thus, with a coarse scale chart, that provides few details of nearshore hazards such as rocks, a thumb's width would represent a great distance, and the ship would be steered far from shore; whereas on a fine scale chart, in which more detail is provided, a ship could be brought closer to shore.^[5]
'Statistics'
The Statistical Rule of Thumb says that for most large data sets, 68% of data points will occur within one standard deviation from the mean, and 95% will occur within two standard deviations. Chebyshev's inequality is a more general rule along these same lines and applies to all data sets.
'Hazardous Material Emergency Response'
Hazardous material (hazmat) emergency responders in the US are trained to various levels of capability for action during a hazmat incident, with names for the capabilities varying by locale. Typically, basic-level responders are trained to be able to recognize various types of hazardous materials and establish an isolation perimeter around the site of the incident. Basic-level responders will observe the "Rule of Thumb" for establishing a minimum safe distance from a hazmat site. If the responder is uphill and upwind from the incident, and they are able to visually cover the site with a thumb held at arm's length, they are assumed to be a safe distance away from the event. Of course, this varies greatly depending on the nature of the hazmat incident, and should only be used as a general guideline. More specific information about hazardous material isolation is available in a material's material safety data sheet, or in such documents as the Emergency Response Guidebook, published by Chemtrec in the US. Other countries typically have their own hazmat emergency response resources.

References

1. http://www.phrases.org.uk/meanings/307000.html
2. http://www.canlaw.com/rights/thumbrul.htm
3. Sir William Blackstone, Commentaries on the Laws of England (New York: W. E. Dean, 1836), vol. 1, p. 36.
4. Elizabeth Pleck, "Wife Beating in Nineteenth-Century America," Victimology: An International Journal 4 (1979): 71.
5. http://www.sailchannelislands.com/Nav/navx_thumb.php

External links

★ A collection of various Rules of Thumb - A wiki based collection of user submitted rules of thumb

★ Straight Dope - Discussion of the origins of the term by Cecil Adams.

See also

★ Heuristic argument

★ Common sense