Abstract: A method of determining characteristics of a rotary drag-type drill bit comprises the steps of: creating a computerized representation of the cutters on the drill bit, and then, with each cutter in turn, projecting the shape of the cutter onto a fixed plane having an array of cells, and assigning a first marker to those cells of the array which overlie the projection of the selected cutter. The representations of the other cutters are then rotated about the bit axis until they have all passed through the plane at least once, the cutters also being moved axially while being rotated so as to represent the axial movement of the bit during drilling. The shapes of the other cutters are projected onto the plane, as they pass through it, and a second marker is assigned to those cells of the array which overlie both the projection of the selected cutter and the projections of any of the other cutters.