If you are unaware, they have two gearboxes, one behind the other. Basically you go through the gears in the "main" then shift the auxiliary up a gear, then start all over in the main. "Sort of." Because there are certain combinations of the two gearboxes that cause overlap, that is nearly equal ratios with some other combination of the two, some combos are skipped. 3x4, 4x5 gearbox, etc