Total Track is defined as the distance between the vertex of the surface furthest left (minimum z coordinate) and the vertex of the right-most surface (largest z coordinate). In axial systems, this accounts for all surface thicknesses from surface 1 to the image plane.

This definition holds even when being applied to systems that are non-axial. For example, the Total Track length is indicated in red on the diagram below of a singlet followed by a fold mirror, reporting the distance from surface 1 (the stop) to the center of the fold mirror. Thus, this metric has little or no meaning for these types of systems.