Rules of Thumb - For Everything

Use ƒ16 at the reciprocal of the film speed on a sunny day when you don't have a light-meter.

clipped from rulesofthumb.org Try this: Count the number of times a cricket chirps in 15 seconds, and add 37. No, you didn't just calculate your age in cricket years - you measured the temperature outdoors in degrees Fahrenheit. You just used a rule of thumb. A rule of thumb turns information you have into information you need. The goal of this website is to gather every rule of thumb on earth into one gargantuan, easily searchable online reference database that will be accessible from anywhere in the world and continue to grow forever. 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. they give you a feel for a subject. It is not a Murphy's Law. Murphy says that things will take longer than we think; a rule of thumb says how much longer.