“A rule of thumb is a homemade recipe for making a guess. It is an easy-to-remember guide that falls somewhere between a mathematical formula and a shot in the dark. A farmer, for in­stance, knows to plant his corn when oak leaves are the size of squirrels’ ears. An economics profes­sor knows from sad experience that inviting more than 25 percent of the guests for a univer­sity dinner party from the economics depart­ment ruins the conversation. Rules of thumb are a kind of tool. They help you appraise a problem or situation. They make it easier to consider the subtleties of the topic at hand; they give you a feel for a subject.” —RulesOfThumb.org

What are yours?