003 Abbe

Measure things as close to their action as possible.

• Proposed by the German physicist Ernst Abbe.

• Abbe errors are angular errors that increase with distance. For example, wobble from a bent axle increases with the length of the axle. The Abbe principle prevents this type of error.

• The Abbe principle states that the best measurements are achieved when taken as close to the action as possible. For example, placing a temperature sensor near a heat source will result in more accurate measurements than a sensor placed farther away.

• The principle also has implications for the design of mechanisms. Actuators and bearings should be placed as close to lines of action as possible.

• Consider the Abbe principle in measurement, and the design of mechanical systems and structures. Locate measurement devices and components as close to the areas of action as possible.

See Also Error • Redundancy • Saint-Venant’s Principle

A caliper that measures in its line of action (top) is more accurate than a caliper that measures away from its line of action (bottom).