Sock Machines: How do you know which stitch will rib?

I watched my Legare 400 ribber and figured out that "four needles under" was how to know where to switch it in or out -- the fifth needle under the working part of the ribber gets put into work (or taken out of work) when I reverse the switch. Yours may be different. So I just make sure to place it where I want it on that "fifth needle" counting from the leading edge of the ribber, where it covers the needles as it moves around.

(posted by me this day on sockknittingmachinefriends)