Turing Tumble is a fun game and highly recommended. I kept accidentally dropping a marble into the play field and when I would scramble to catch it that would inevitably trigger another marble from a random side to be released. Soon there are marbles moving in every direction on the board and off. To prevent the computer from running accidentally I designed a part which prevents the clocking arms from moving while the board is being manipulated either from dropped marbles or the occasional brush with the "Push to Start Tab".

This is similar in concept to https://www.thingiverse.com/thing:3323584. I just did not know this thing existed before making my own.