The problem with Ref. 5959 is that it is not water resistant, where Ref. 5950A is water resistant, and it also compliments Ref. 5951P. Ref. 5959P is the only modern, and current Split Second Chronograph that is not water Resistant, unlike 5004, 5204, 5950A, 5951P. Water Resistance is an important aspect of a watch whenever possible. The big reason Ref. 1463 Vintage Chronograph is so popular, more costly than Ref. 130, and (many Ref. 1579), and 533, 591 (1506,530) is because it is water resistant, and 1563 also being a split second and water resistant.