In order to compare saddle backwardness as a reference point, it is not necessary to take the tip of the saddle (each saddle has a different length) but its anatomical center is located where the saddle surface is wide 7.2cm. Qunindi saddle saddle by convention is the distance between the center movement (c / c) and the anatomical saddle center
Most fitters do not use “anatomical” center because fits are personal and that is still arbitrary. Setback according to Retul/BG and Guru is the horizontal distance from saddle tip to BB-center. That is fine because the assumption is made that a saddle has already been selected. It is a coordinate used to replicate your fit on different bikes using the same saddle.