Wonderful toy for everyone who took Fred Thompson's "Foundation of Mathematics"* course at Caltech in 1970-71. I worked out so many examples of Turing Machine operation, on paper, by hand, filling notebooks with 1's and 0's. Then proving that Turing Machines == Church's Grammars == general recursive function theory as part of the final test (my only "A" in math in four years at Caltech). The amazing thing is that this machine is slower than I was! (Although it's orders of magnitude neater.)

*Yeah, I know ... it had a different name, but this is the name that Professor Thompson wanted to name it by the time he finished the year.