How does a viewmaster disc drive forward?

I'm coming down with a cold. As I'm writing this two days after the posting date, I think that is the reason I'm feeling low all week, generally uninspired and moody. Even the end of term doesn't bring a spring to my step. Geremy showed me his new computer cutting device which should be able to cut precise viewmaster slide holders. The results so far have not worked perfectly, but it is likely a matter of time and selection of the correct paper stock. To me, the mystery is how the disc is driven forward and whether or not that aspect of the disc needs to be enhanced. With the older (familiar) viewmaster viewers, you cannot see the drive device. However, with the newest model, the disc seating area is visible from the top and it is readily apparent that the drive is done solely with the cut notch set every second frame.
Undergrad classes ended. Grading won't take too long.