There are two different styles of read heads, one has “2X” stamped in the case (P/N 93-0414) the other does not (P/N 50-0020).
There are two different interpolation boxes that are used for the specific read head. The interpolation boxes are not interchangeable between the different styles of read head. Read head 50-0020 (the unmarked read head) must use the 50-0019 interpolation box and 50-0020A (2X read head) must use 50-0019A. The following table describes the position of the DIP switches. These must be set correctly in order for the linear scale to function correctly.