The included angle of a V-groove on a large ceramic workpiece with a length of 500 mm is measured on an ultra-precision surface grinding machine. A pair of electronic dial gauges is mounted on the grinding wheel head to detect the ground flank surfaces of the groove. A calibrated artefact with identical material and nominal geometry but a shorter length of 100 mm is aligned side-by-side with the workpiece. The influences of machine scanning motion errors and thermal errors on the angle measurement are compensated through measuring the angular deviations of the V-grooves on the workpiece and on the artefact.