<P> According to phrases.org.uk, "The phrase joins the whole nine yards as one that probably derives from some form of measurement but which is unlikely ever to be definitively pinned down ." </P> <P> The term is thought to originate with carpenters who used the length of the tip of their thumbs (i.e., inches) rather than rulers for measuring things, cementing its modern use as an imprecise yet reliable and convenient standard . </P> <P> It is often claimed that the term rule of thumb is derived from a law that limited the maximum thickness of a stick with which it was permissible for a man to beat his wife . English common law before the reign of Charles II permitted a man to give his wife "moderate correction", but no rule of thumb has ever been the law in England . </P> <P> Belief in the existence of a "rule of thumb" to excuse spousal abuse can be traced as far back as 1782, the year that James Gillray published his satirical cartoon Judge Thumb . The cartoon lambastes English judge Sir Francis Buller for allegedly ruling that a man may legally beat his wife provided that he used a stick no thicker than his thumb, although there is no other written record of Buller making such a pronouncement . </P>

Where does the rule of thumb come from