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Inv. 52869 - Descriptive notes

The rim is rivetted to the back plate. The zeroes on the plates have been punched very forcefully and often are a dark circle rather than a ring; the impressions are clearly visible on the reverse. The throne has been damaged, perhaps during repair or reattachment of a shackle. There is a recess in the rim at the throne, perhaps to allow a pinion to be installed to engage with the toothed rete. However, there is no evidence on the back plate of a hole for an arbor.

The plates show construction lines and points: for 42, 48 and 51 degrees the right line with centre points for marking azimuths is clearly visible. Intersections for defining the almucantars and various centres for circular arcs are also visible.

On the meridian line of the plate for 45 degrees a user has very lightly scratched elevations for the almucantars from 25 to 60 or 65 degrees (after which point there is no longer space for numerals). The numerals are simple and open in appearance, perhaps from considerably later than the date of construction. Presumably they were added by a user whose latitude was somewhere near 45 degrees (though the numerals are so faint that they may not have been very helpful in reading off values).

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