# Airy points

Airy Points are used for precision measurement (metrology) to support a length standard in such a way as to minimise bending or droop. The points are symmetrically arranged around the centre of the length standard and are separated by a distance equal to

$1/\sqrt{3}=0.577...$

or approximately 5/9ths of the total length of the measuring device.

Airy points are normally identified by inscribed marks or lines. For example, a 450 mm length gauge would have an Airy point separation of 450 mm times 5/9 = 250 mm. A line or pair of lines would be marked onto the gauge 100 mm in from each end. Supporting the artifact at these points ensures that the calibrated length is preserved. If the length gauge is not supported at the Airy points, the measurement uncertainty is increased.