# 2400 BCE—1820 CE Computing devices

## Suanpan

Beads above the beam are heaven beads; beads below the beam are earth beads. Use four earth beads and one heaven bead on each rod to count in tens. Use five earth beads and two heaven beads to count in sixteens for units of weight. Cultivate thoughtlessness to perform calculations with minimal thought.

## Antikythera mechanism

It used the Sothic Egyptian calendar and predicted the Olympic-game cycles, the positions of sun and moon, twenty-seven eclipses of the sun, and thirty-eight eclipses of the moon, various calendar cycles, and possibly positions of the five known planets. Egyptian names for thirteen months are transcribed in the Greek alphabet. Corinthian names for twelve lunar months are on the perimeter of the Metonic dial. It shows the path of the ecliptic through the twelve houses of the zodiac labeled by their Greek names and keyed to specific stars. It computes the Metonic cycle, the Saros cycle, the Olympiad cycle, the Callippic cycle, and the Exeligmos cycle. It tracked the precession of the elliptic. It used epicyclic gearing to track the eliptical orbit of the moon. It used a differential gear to track the phases of the moon. Nevertheless, its conception was finer than its manufacture, so that the subtleties it was designed to show would have been swamped by the crudeness of its gearing.

## Napier’s bones

Here we have a set of multiplication tables arrangeable on a board to calculate products and quotients of large numbers. They are like toys but without a childish stigma, reducing multiplication to addition and division to subtraction.

## Slide rule

The modern Acu-Math No. 500 has nine linear logarithmic scales, three scales on each part, and three parts, the center free to slide. The alignment of scales is assisted by a sliding transparent hairline cursor. It multiplies and divides, finds logarithms and exponentials, finds squares and square roots, cubes and cube roots, finds sines and cosines, tangents and cotangents, does unit conversions and conversion to natural logarithms. The modern Acu-Math No. 500 introduced in 1960, is obsolete.