A method of determining any offset between: a scale axis of a disc scale member having a planar surface on which is provided a series of scale features defining a scale that extends and is centred around the scale axis, the scale axis extending normal to the planar surface; and the axis of rotation of a machine part on which the disc scale member is mounted, wherein the axis of rotation and the scale axis of the disc scale member are substantially parallel. The method includes: determining any offset between the scale axis and the axis of rotation via inspection of an axially-extending surface provided with the disc scale member.