There are four knobs on the top. Are the two small knobs for camber only or are the used in squaring the chisel on the jig? If I place my chisel into the jig hard against the right edge which is the reference edge, opposite the two small knobs; my chisel is not 90 degrees ie square to the grinding wheel. I have used the two small knobs to square my chisel. If it is not square then applying "camber" to it will also square it. Of course there is no camber but I want a square chisel. Overextending the camber adjustment will make a camber and too much will make it so that you cannot slide the jig on the support bar.