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Today I revisited the Guildhall clock Museum and
can confirm that the Elias Allen dial has no facility to take a vertical post to
cast a shadow which could indicate the sun's azimuth. There are no fixing
holes, and anyway the compass rose is centered within the base of the gnomon.
The reason the rose shows reciprocal compass points (i.e out by 180 degrees )
remains a
mystery.
Geologists talk of magnetic reversal of the Poles though I suspect this was a
bit before the time of Elias
Allen! John
Moir
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