(EN) The invention relates to a locking system comprising a lock cylinder for an inner track key comprising at least two coded tracks (61, 62) on one side of the key (60) and a number of plate tumblers (40) are arranged in a cylinder core (30). In order to improve four-track locking systems of this type, the height ratios between the maximum progressive ratio hcode 1 (71) of the first coded track (61) of one key side, the maximum progressive ratio hcode 2 (72) of the second coded track (62) of the same key side, the key height hS (76) and the height hT (74) of the partial areas (42) on the plate tumblers (40) are selected such that they satisfy the equation hcode 1 (71) + hcode 2 (72) + hT (74) > hS (76). This measure completely prevents the ability to pick inventive locks of this type using known tools for breaking in, e.g. a 'Little Joe' tool. The invention also provides that all partial regions (42) of the plate tumblers are assigned to one side of the lock cylinder and each second plate tumbler is loaded in a direction toward the cylinder jacket that is opposite the direction of the spring loading of the preceding plate tumbler.
