Patented by W. Keister 1972, made by Binary Arts / Think Fun.
(top: plastic, 12.25 inches;
bottom: plastic, nnn inches))
There is a bar with knobs on it in a track.
There is only one position along the track where a knob can be turned.
When all of the knobs are turned horizontal
(curved end to the left in the photo above)
the bar can slide all the way out.
There are only two possible moves at each point, and so to solve,
one can repeatedly choose the move that does not return the puzzle to the previous position.
Start by turning the rightmost knob.
The original version is shown first above.
which became Think Fun,
later made the one shown second above,
which allows the knobs to be reset
(by flipping down the end and sliding out the bar);
this one was purchased in 2008.
presents this puzzle,
which is essentially the same puzzle as the
(described in another Keister patent)
(see that page for information about Gray Codes and additional links).
from: www.uspto.gov - patent no. 3,637,215