Rule of thumb
A rule of thumb (also a rule of thumb ) is a method for the fast determination of a mathematical or technical value without performing precise engineering calculations. The origin of the name is unclear. The synonym rule of thumb is a loan translation from English rule of thumb.
The calculations, which involves a rule of thumb, always so simple that it can be determined quickly by mental arithmetic. Most rules of thumb resulting from experience.
One can distinguish between rules of thumb, experience, values characterize without there ever an exact calculation procedures, and rules of thumb that allow assessments when the exact calculation would take too long or in the head not feasible ( phrase " rule of thumb " ) would be. Scientifically rules of thumb in cognitive science, artificial intelligence and computer science will be examined under the term heuristic.
Examples
Minutes to sunset
It forms a fist and counts the number of fingers that fit with an outstretched arm, between the sun and the horizon. The result is multiplied by 8 minutes.
Distance estimation by means of the thumb jump
The thumb jump is a rough method for estimating the distance of the measured person to a stationary object, the width of which is known.
Distance of lightning
The rule of thumb (one third of the distance from flash of light and thunder in seconds) for the distance of a lightning strike in kilometers is:
The result differs from the actual distance depends on ambient temperature, since the speed of sound does not correspond exactly 1/3 kilometers per second.
Motor vehicle physics
A rule of thumb for the stopping distance, which is explained in the local paper is the following:
The formula makes use of the fact that the speedometer indicates the speed in increments of 10, and the bill is particularly simple.
Chemistry
In chemistry often (sometimes more mockingly ) stated that all ( inorganic ) white powder have approximately the density of 2.3 g / cm ³ and having no flammable liquids having a density of 0.8 g / cm ³.
Rather than rule of thumb is meant Van't Hoff's also the rule that says that the reaction rate of a chemical reaction approximately doubles for each 10 K increase in temperature.
Economics
In business considerations, the Pareto rule or 20/80-Regel be used, stating that often already pronounced to about 20 % strength unfolds cause 80 % of the possible effect in cause-and- effect relationships. Examples: With 20 % of customers are 80% of sales generated, 20 % of the products are responsible for 80 % of the complaints, 20 % of the causes of errors draw 80 % of the errors according to 20% of the means of production are responsible for 80 % of the cost. Based on these considerations, optimization processes are generally limited to the main causes.
Compound interest
The 72 rule states that, will double the value of an investment after 72 years, divided by the interest rate in percent.
Instead of the interest rate can also, for example, suspected for the duration of inflation can be used to predict the loss in value. So a unverzinster amount of money at 10 % inflation in 7.2 years would lose half of its purchasing power after the 72 rule.
Decision Theory
With the 37 % rule, a time when the decision is to be found in order to find the optimal element.