If you can believe it, there was a time when humans did all kinds of complex computations without computers. This desktop gadget is a prime example, available in two sizes as a replica of a tidal abacus from 1570 that currently resides in a museum. It uses the moon to calculate the tidal cycles, and on the large model, the back side is a nocturnal dial that uses fixed stars to tell the time. Both dials are accurate, fully functional tools that don't require an electrical outlet, and each size features a Sapele mahogany base. The piece comes with detailed information about how to use the dial and its history and is made in Spain.