Slide Rule (1940 - ) was a Thoroughbred race horse who was owned by William E. Boeing of Boeing. He sired by Metropolitan and Suburban Handicap winner, and was out of the mare King's Idyll, a daughter of the outstanding Champion sire and broodmare sire, Sir Gallahad III. He was a stablemate of the morenoted , and in April 1943, of the colt Twoses. Newspaper reports of the early 1940s described him as a little chestnut colt.