Since I do not know if Tascam released a Auto Reverse reel deck- maybe some were made for broadcast in Japan, but I have found that in many of then there is this large difference between the forward direction and reverse direction with regard to speed. This is with all rollers oiled and capstan bearing oiled and clean pinch rollers and capstan shafts. There has not been a way to correct for this until I came up with this mod that allows each speed and direction to be adjusted independently for pretty good perfection. This new board attaches to the servo board and is wired into it. So far the two cases where it has been applied have worked very well. My final design will employ multi-turn trimmers for even better control. This can actually apply to most X series deck that are not the half track versions- the 1/2 track decks do not have reverse direction.