Additional method for measuring long tubes (leap-frogging)

Currently the only method available for measuring long tubes (leap-frogging) is the "Move Tube" where it is required to measure two straights. If all straights are just too big to allow for selection/measurement of any two, this obviously won't work. Perhaps we can add an additional method, similar to that of G-Tube, where we add a displacement T-square, perpendicular to any straight.