Carol I will be honest with you I have not figured out all of the feature my 500 has and it has the same type of knobage going on. From what I have gleaned from what little I have read about them is you can change knob positions and the stitches with change even if you do not change the cams. I think there are only 5 cams for these machines and an endless amount of decorative stitches can be made from them.
After I get to playing with my 500 I will have a little more understanding of what does what on the guys. I am more into the treadles and the machines from the 40's back.
Billy