According to the invention, a method for determining the radial position of a rotatable object is disclosed. The method may include providing targets at known relative radial positions coupled with the object, where a radial distance between any two adjacent targets is substantially not equal to the radial distance between any other two adjacent targets. The method may also include rotating the object about an axis, where the distance of the rotation is believed to be known. The method may further include determining, during rotation, that a first target is in proximity to a point fixed relative to the axis. The method may additionally include determining, during rotation of the object, that a second target is at least in proximity the point fixed relative to the axis. The method may moreover include comparing of the believed known rotation with the known relative radial positions of the plurality of targets.