I am not very well versed in it, but, in the second pidture, see the little black discs in the top of the accessory box? Those are cams. Also in the second picture I have a little door on top opened, that is where you put the cams. They make the stitches different. You have one for zig-zag, another for another stitch and I think, at times you put two at a time....dunno for sure.