Computers read the (optional) frame offset (marked every four perforations on actual film by a single "-" dash) by adding digits to the Keykode after the plus sign. In this case, a frame offset of two frames (with respect to the film foot) is specified. The number of frames within a film foot depends on both the film width and the frame pulldown itself, and can also be uneven within the same roll, but rather repeat periodically (like in the 35mm 3perf. pulldown).