To use the dial, the sliding ring is set to the latitude and the alidade is set to the declination. The instrument is then suspended and the disc is turned until the sights are directed towards the sun. The distance between the notch on the sliding ring and the notch in the centre of the zodiac scale is measured by a small ruler, where the time may be read directly.

Museum of the History of Science, Oxford
Inventory number 34394

© Museum of the History of Science, Oxford. All rights reserved. Information and images provided here may not be reproduced in any form or by any means without the prior written permission of the museum.

Basic URL: http://www.mhs.ox.ac.uk/epact/catalogue.php?ENumber=71952