Abstract: A calculating device and a method of use thereof for determining the lead required to shoot a projectile at a moving target including cooperating logarithmic scales with indicia corresponding to the parameters target speed, range, projectile speed and lead displayed on a fixed and a slide member. Pictorial markers representative of various projectiles are disposed along the projectile velocity scale at locations corresponding to their normal speed and words descriptive of target speed are disposed at appropriate locations along the target speed scale so that calculations may be made by persons not having knowledge of game and projectile speeds in numerical terms. In accordance with one embodiment of the invention, the logarithmic scales are longitudinally disposed and the slide member may move relative to the fixed member in a horizontal direction. In accordance with other embodiments of the invention, the scales are disposed in a circular arc on members which may be rotated about a common axis.

Abstract: A calculating device and a method of use thereof for determining the lead required to shoot a projectile at a moving target such as game including cooperating logarithmic scales with parameter indicia corresponding to the range of the target, the speed and direction of movement of the target, the speed of the projectile and the required lead displayed on a fixed and a slide member. Markers representative of various projectiles are disposed on the projectile velocity scale at locations corresponding to their normal speed and words descriptive of game speed are disposed at appropriate locations along the target speed scale so that calculations may be made by persons not having knowledge of game and projectile speeds in numerical terms. The lead is calculated from a knowledge of the parameters in a two step process of moving one member relative to the other. In accordance with one embodiment of the invention, the scales are arcuately disposed on members which may be rotated about a common axis.