A rule of thumb is a heuristic guideline that contains simplified guidance or a set of ground rules on a particular topic or approach. It is a general principle that gives practical instructions on how to perform or approach a particular task. As a rule, rules of thumb develop as a result of practice and experience and not through scientific research or a theoretical basis. 1. www.oed.com/view/Entry/168726 ^ 2. www.straightdope.com/columns/read/2550/does-rule-of-thumb-refer-to-an-old-law-permitting-wife-beating ^ If Hercules` great stature could be guessedBut by his thumb, the index finger of the rest,In a reasonable proportion, the best rule, the IWould falls to measure the beauty of Venus,Should be his leg and foot: A modern folk etymology states that the expression is derived from the maximum width of a stick, which according to English customary law for the beating of Wives are allowed. but such a law never existed. This belief could stem from an eighteenth-century statement by Judge Sir Francis Buller that a man can beat his wife with a stick no wider than his thumb. The rumor produced many satirical jokes and caricatures at Buller`s expense, but there is no indication that he made such a statement. Nor is it true that a husband has the right to whip his wife.
And if he had, it`s not easy to see how the thumb is the size standard for the instrument he can use, as some of the old authorities said. The norm is the effect created and not the way it is created or the instrument used.  : 41-42 This is not the case. While it is true that English common law once stated that it was legal for a man to punish his wife in moderation (whatever that meant), the “rule of thumb” in England was never the law. « Many of the deepest Christians love foolish builders who build according to conjectures and rules of thumb rather than squares and rules. » A good rule of thumb is to use less than 10% of the balance at your disposal. [The snack] Investors may be familiar with a variety of “financial rules of thumb” designed to help individuals learn, remember, and apply financial policies. These rules of thumb deal with methods and procedures for saving, investing, buying a home, and planning for retirement. While a rule of thumb may be suitable for a wide audience, it may not apply universally to every individual and every unique set of circumstances.
For example, the common law doctrine had been amended to give the husband “the right to whip his wife, provided he uses a switch no bigger than his thumb” – a rule of thumb, so to speak.  The term rule of thumb was first associated with domestic violence in the 1970s, after which the misconception was cited as factual in a number of legal journals, and the U.S. Civil Rights Commission published a report on domestic violence in 1982 titled “Under the Rule of Thumb.” Some efforts were made to discourage the phrase, which was considered taboo because of this false origin. In the 1990s, several authors correctly identified the wrong etymology; However, the link with domestic violence was cited in some legal sources even until the early 2000s. However, a rule of thumb that beats wives has never been codified by law.   : 15 Contrary to the old myth that is now prevalent on the Internet, the origins of the rule of thumb have nothing to do with beating wives, so the phrase is not inherently offensive (although the fact that some people think it is offensive may be a reason to use it with caution).2 The phrase is also found in Sir William Hope`s The Compleat Fencing Master, 1692: “What he does, he does according to the rule of thumb and not according to art.”  James Kelly`s The Complete Collection of Scottish Proverbs, 1721, contains: “No Rule so good as Rule of Thumb, if it hit”, which means a practical approach.  At the end of the 20th century, some efforts were made to discourage the rule of thumb, which was considered taboo because of this false origin.  Patricia T. . . .