Editing Rule of thumb (section)

== Origin and usage ==
The exact origin of the phrase is uncertain.{{r|Martin}} Its earliest (1685) appearance in print comes from a posthumously published collection of sermons by Scottish preacher [[James Durham (minister)|James Durham]]: "Many profest Christians are like to foolish builders, who build by guess, and by rule of thumb (as we use to speak), and not by [[Square (tool)|Square]] and [[Ruler|Rule]]."{{r|OED|O'Conner}}

The phrase is also found in Sir William Hope's ''The Compleat Fencing Master'' (1692): "What he doth, he doth by rule of Thumb, and not by [[Art (skill)|Art]]."{{r|Safire 2003}} James Kelly's ''The Complete Collection of Scottish Proverbs'', 1721, includes: "No Rule so good as Rule of Thumb, if it hit",{{r|Kelly|James Kelly}} meaning a practical approximation.{{r|Safire 2003}}
[[File:Width_of_man's_thumb_one_inch_ruler.png|alt=Man's thumb on a wooden ruler that is marked in inches|thumb|An adult's thumb is about one inch wide, so it can be used to estimate the size of an object.]]
Historically, the width of the thumb, or "thumb's breadth", was used as the equivalent of an [[inch]] in the cloth trade; similar expressions existed in Latin and French as well.{{r|O'Conner|Kelly}} The thumb has also been used in [[brewing]] beer, to gauge the heat of the brewing vat.{{r|Wordsworth}} [[Ebenezer Cobham Brewer]] writes that ''rule of thumb'' means a "rough measurement". He says that "Ladies often measure [[yard]] lengths by their thumb. Indeed, the expression 'sixteen nails make a yard' seems to point to the thumb-nail as a standard" and that "Countrymen always measure by their thumb."{{r|Brewer}} According to ''Phrasefinder'', "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."{{r|Martin}}