This is what Peter says about the PTP3
"The first time you use it you must find the correct setting for 45 and 33, using a strobe and slowly moving the small screw in the slit in the right front corner. Once you have found the right setting you can use the speed stops (the keyhole shaped bits under the platter) to secure the settings so you can return to them every time. If you download the PTP assembly guide you can see these parts a bit better."
I was not aware the platter had to be removed on either PTP3 or PTP4 to make a speed change.
I am wondering how OMA PTP slate decks are doing it. I don't know, but it doesn't seem like loosening, moving and tighening a hex screw to make speed changes would be a viable option on a high end consumer deck.