Accurate Linear Scales Ruled on a Grating Engine*

Abstract

The absolute spacing ruled by a grating engine is determined by ruling a linear scale and using it as a diffraction grating. The angles of incidence and diffraction are measured with a spectrometer. After the wavelengths are adjusted to the experimental conditions, the average spacing of the scale is calculated from the grating equation. Wavelength standards are thus used directly for determining line standards of length.A procedure is described for calculating the engine setting to rule a scale with a desired spacing. A three-inch scale ruled according to this procedure has been certified by the National Bureau of Standards, the certification agreeing with the calculated value for its length to within ten microinches.