The Preludin Calculator, for determining height-weight ratio in accordance with sex and age, metal with plastic cover, in cardboard case, British, c. 1960.

The slide rule calculator was distributed to medical professionals in order to help calculate when a weight loss drug, Preludin, should be prescribed. The drug Preludin was part of the amphetamine family, and was often used recreationally as a party drug. It had been withdrawn from the market by the 1970’s.

A person’s height to weight ratio in accordance with sex and age was determined using this calculator. It was simple but effective. The calculator was used in large scale health studies. Two interlocking circular tubes adjust to line up age, weight and height in small cutaway windows. The calculator indicated how overweight the subject was by aligning these variables. The Preludin Calculator is the forerunner to today’s body mass index (BMI) charts. This simple grid assesses your ideal weight. It is not fool-proof. The Preludin Calculator and the BMI charts put many athletes in the obese category because muscle weighs more than fat.