The pulley/cam system also confers a benefit called "let-off." As the string is drawn back, the cams rotate. The cams are eccentric rather than round, and so their effective radius changes as they rotate. Each of a compound bow's two cams features two tracks: an inner track which connects to the opposite limb or opposite cam through cables, and an outer track through which the bowstring runs. As the bow is drawn, the ratio of bowstring pay-out and cable take-up relative to limb-weight and leverage of the cams changes. By manipulation of the shapes of these cam tracks, different draw-stroke profiles can be created. A compound bow can be soft-drawing with a slow build-up to peak weight and a gradual let-off with a long "valley" at the end. It can also be hard-drawing with a very fast build-up to peak draw-weight, a long plateau where weight is maintained, and a quick let-off with a short valley. The let-off itself is the result of the cam profiles having passed center and approaching a condition very similar to a cam-lock. In some compound bows, if the draw-stops or draw-length modules are removed, they will self-lock at full draw and require professional equipment to unlock safely. Many compound bows offer 70–85% let off once they are pulled to full draw. This allows the shooter to relax and concentrate on the intended target at which they are shooting.