1. A method for estimating, for an ophthalmic lens grinding machine ( 1 ), the angular offset (δ) between a rotating radial axis (Y) associated with a lens that is to be ground and a reference rotating radial axis (Y′), said grinding machine ( 1 ) comprising: a grinding wheel ( 3 ); a support shaft ( 5 ) that can rotate about its axis (X) and can move with respect to the grinding wheel ( 3 ), on which support shaft an ophthalmic lens ( 7 ) can be mounted via a grinding adapter ( 15 ), such that the lens rotates as one with the shaft, drive means ( 9 ) designed to rotationally drive the support shaft ( 5 ) about its axis (X) and to move the support shaft ( 5 ) with respect to the grinding wheel ( 3 ); and control means ( 11 ) able to control the drive means ( 9 ) according to a preprogrammed control law connecting the relative position (r) of the support shaft ( 5 ) and of the grinding wheel ( 3 ) to the angular position (θ) of the reference rotating radial axis (Y′) in a fixed frame of reference connected with the axis (X) of the support shaft ( 5 ); which method comprises: grinding a reference standard lens ( 31 A) on which the radial axis (Y) associated with the lens has already been embodied in the form of a line, according to a control law corresponding to a theoretical finished shape of reference standard lens, of which the theoretical inclination of a reference part ( 33 A) of the contour with respect to said reference radial axis (Y′) is known; producing an image ( 31 AI, YI) of the finished reference standard lens and of said line; analyzing said image ( 31 AI, YI) using image-analysis means, so as to measure the actual inclination (δI) of the image ( 33 AI) of the reference part ( 33 A) with respect to the image (YI) of the line; and deducing said angular offset (δ) which is equal to the discrepancy between the measured actual inclination (δI) and the theoretical inclination.