In the movie “Boondock Saints”:http://imdb.com/title/tt0144117/, one of the main characters makes a feminist gaffe by referring to a something as a “rule of thumb.” A woman who overhears him gets pretty irate and cites a “since debunked”:http://en.wikipedia.org/wiki/Rule_of_thumb#Origin_of_the_phrase rumor that the origin of the term comes from a British judicial decision and if memory serves me correctly, punches him in the face.
Whatever its origin, a rule of thumb is a useful and easy to learn guide not to be taken literally. Every field uses rules of thumb in some way and this very useful “website”:http://rulesofthumb.org/ has some of the best. For example, here are two rules picked from disparate fields:
Anthropology:
??The number of people occupying a house in a preindustrial culture can be estimated at one person for every ten square meters of enclosed dwelling space.??
Astronomy:
??You can describe the location of objects that are low in the sky by holding your hand in front of you at arm’s length. With your palm facing in and your pinkie on the horizon, the width of your hand covers 15 degrees of arc above the horizon.??