Abstract: A calculating device for use in conjunction with past performance data conventionally compiled and published on each active thoroughbred horse performing on U.S. racetracks, has three cooperating transparent slides each indexed visibly in terms of racehorse racing time and in speed ratings. The first, or innermost, slide is compound, with time and rating scales and time and distance columns on its obverse face, and assigned weight, age, post position, calendar, track condition and class data expressed in time difference increments on its reverse face. A second slide surrounds the first, and carries a speed rating index extending along the direction of slide motion. An outer slide movable relative to both others has transverse index lines based on seconds of time as expressed on the innermost slide and a table of conventional time performances for various segments of various races.