Airy points
support points chosen to minimize the distortion of the length of a physical standard
Airy points (after George Biddell Airy) are used for precision measurement (metrology) to support a length standard in such a way as to minimise bending or drop of a horizontally supported beam.
Choice of support points
A kinematic support for a one-dimensional beam requires exactly two support points. Three or more support points will not share the load evenly (unless they are hinged in a non-rigid whiffle tree or similar). The position of those points can be chosen to minimize various forms of gravity deflection.
A beam supported at the ends will sag in the middle, resulting in the ends moving closer together and tilting upward. A beam supported only in the middle will sag at the ends, making a similar shape but upside down.
Airy points
Supporting a uniform beam at the Airy points produces zero angular deflection of the ends. The Airy points are symmetrically arranged around the centre of the length standard and are separated by a distance equal to
1
/
3
=
0.57735...
{\displaystyle 1/{\sqrt {3}}=0.57735...}
of the length of the rod.
"End standards", that is standards whose length is defined as the distance between their flat ends such as long gauge blocks or the mètre des Archives, must be supported at the Airy points so that their length is well-defined; if the ends are not parallel, the measurement uncertainty is increased because the length depends on which part of the end is measured.
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This entry incorporates text from “Airy points” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.