Pocket sundial from 2nd century AD Rome. Inside, on an axis, was a pointer and 4 discs, each with 2 diagrams on the front and back, showing different polar altitudes. It had to be held so that the sunbeam shone through the slit in the side, and the time could then be read on a scale [1715×2278]

Pocket sundial from 2nd century AD Rome. Inside, on an axis, was a pointer and 4 discs, each with 2 diagrams on the front and back, showing different polar altitudes. It had to be held so that the sunbeam shone through the slit in the side, and the time could then be read on a scale [1715×2278]

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