Abstract: A sensor having a mass that moves relative to a structure is disclosed. The mass is attached to the structure by a rigid member such that the mass moves around a pivot point on the structure, the pivot point remaining fixed with respect to the structure as the mass moves. A code scale is attached to the mass. An imaging system that is fixed with respect to the structure forms an image of the code scale. A controller provides an indication of a position of the mass relative to the structure using the code scale image. The rigid member can include a surface having the code scale thereon, the surface rotating about the pivot point as the mass moves such that the surface remains at a fixed distance from the pivot point as the mass moves.