Spin the gears until every column reads 42.

Spin the gears until every column reads 42.

The wooden frame holds a stack of numbered gears. The puzzle: spin each one until every column adds up to 42 at the same time. Not 42 in one column and 38 in the next. All of them, together.

The Antikythera mechanism did this in bronze two thousand years ago. This one does it in birch, on a desk. The frame is small enough for two hands to turn. The gears click into place when a column lands right. A wrong turn takes the whole stack off, and you start again.

Some people solve it in one sitting. Some people solve it over a week, leaving it on the bookshelf as a conversation piece between attempts. Either way, the puzzle looks good sitting open. It looks even better when you finally close it on the solved position.