Abstract: A calculating device for a bowling game whereby a bowler can readily ascertain an optimum approach starting location for throwing a bowling ball along a path which will maximize the number of pins knocked down. The calculating device comprises a first member having a first hairline and first and second indexes. The first index has indicia corresponding to bowling pin locations expressed in terms of distance from a given location, such as the marginal edge of a standard bowling lane. The second index has indicia corresponding to target marker locations expressed in terms of distance from the given location. A second member is slidably associated with the first member. The second member has a scale having indicia, corresponding to approach starting locations expressed in terms of distance from the given location, associated with the first hairline and second index. A cursor is slidably associated with the first and second members.