Calibration of high-resolution electronic autocollimators against an angle comparator

At the Physikalisch-Technische Bundesanstalt, autocollimators are calibrated with the aid of the WMT 220 angle comparator to ensure their direct traceability to the SI unit of plane angle, the radian (rad). It is shown that high-resolution electronic autocollimators can thus be calibrated with an uncertainty of 0.007 arcsec ( k = 2) in reproducible measurement steps down to 0.005 arcsec. Calibrations in very small measurement steps close to the autocollimators' resolution can inform about possible short-period deviations and resulting aliasing effects in measurements with autocollimators.