For some beamlines, where the X-ray beam is focussed to less than 100 nm spot size, it is necessary to rotate the sample using very accurate rotary axes. The accuracy of these devices is defined in terms of radial, axial and tilt errors. At the Precision Engineering Laboratory of the ESRF, we are able to calibrate rotary stages and spindles in agreement with the ISO 230-7 and ASME B89.3.4 standards, in static mode (step by step, at given position increments) or in continuous motion. This type of measurement is possible through the use of non-contact capacitive sensors (with measuring resolution in the field of the nanometre) and reference spherical artefacts, working under controlled environmental conditions to minimize the influence of thermal instabilities. The setup includes a special granite stage with a gantry, supported by an active anti-vibration system. The presentation will illustrate the measurement principle and some examples of calibrations, including results obtained on a motorized air-bearing rotary stage for which the measured errors are about 20 nm.