The degree to which the helix measurement accuracy of a gear measuring instrument (GMI) can be calibrated on the sub-micrometer order is limited when using a gear artifact. We propose a new method conducting GMI accuracy evaluation using a wedge artifact (WA) whose plane is treated as the tooth flank. This paper reports (i) a method of measuring the WA with a GMI, (ii) theoretical equation for calculating geometric deviation between a helicoid generated around a reference cylinder by the GMI and the plane of the WA, (iii) useful equations for designing the WA obtained from an analysis of the theoretical equations, (iv) a method of evaluating the helix measurement accuracy with respect to the obtained result, (v) the effect of the setting accuracy of the WA on the GMI, and (vi) evaluation result of a GMI helix measurement accuracy using a WA which we fabricated. Finally, sub-micrometer evaluation was found to be possible. (C) 2010 Published by Elsevier Inc.