A Schoty and a Modern PDA: A Handspring Visor, displaying a calculator, next to a schoty.
Design
The design of the schoty is based on a pair of human hands.If you hold out both hands in front of you, palms facing out, you will see that your 2 thumbs are beside each other and 2 sets of 4 fingers spread out from there. Similarily, on the schoty, each row has 2 sets of 4 beads of the same colour on the outside, representing the 2 sets of 4 fingers and the 2 innermost beads of the same colour representing the 2 thumbs.
The "home" position for the beads is on the right hand side. The bottom-most row represents 1s, the next row up represents 10s, then 100s, and so on. So, counting is similar to counting on one's fingers, the beads move from right to left: 1 to 10, and then carrying upwards to the next row.
Annotated schoty: The numbers on the right are multipliers for the beads in the corresponding row. (Click for a larger view).
Careful observers will note that the metal rods, on which the beads slide, have a slight curvature to prevent the "counted" beads from accidently sliding back to the home-position.
