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This is a Java animation, by Bill Casselman, of the differential assembly in the Antikythera Mechanism. Top slider controls the green (Moon) gear; bottom slider controls the purple (Sun) gear. In the Mechanism itself, these inputs were not independent, since they were fixed by the Sun-Moon assembly in the ratio 254 to 19.

The complete ranges of speeds show that, taken out of the Mechanism, this is a true differential. The next one known was invented in the 19th century. To simulate its operation inside the Mechanism, choose moon-gear speed +2 and sun-gear speed -1/8. This will give a ratio of 16, while the actual ratio of speeds was 254/19 = 13.368... .

Return to 4. The differential in the Antikythera Mechanism.

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