J.L. Baudelocque was responsible for one of the first purposefully designed calipers to measure the external pelvic diameters as figured in his L’Art des Accouchenens Paris, 1789.  He emphasized the significance of the antero-posterior diameter of the inlet and introduced the concept of measuring the external conjugate (Baudelocque’s Diameter), measured from the tip of the spine of the fifth lumbar vertebra to the middle of the symphysis pubis, as an index of the true conjugate.