Ivory portable sundial

This is a diptych dial. This means that it is hinged and closes like a book. These were very popular in 17th and 18th century London. This specimen was made in Nuremburg, the centre for sundial trade in the period 1600-1650. The creator, Miller, was an expert and used the Sun face motif as his identifying mark. He would have designed the dial but would not have made it; a case maker, who has also left his mark, would have made the case. He has used ivory which is highly durable yet easily repaired.
 

On the inner face of the lid is a vertical dial with a thread/string gnomon. The gnomon is made from string (the original is lost and would have been kept in the side of the dial). It had to be set at different angles to keep accuracy depending on the latitude.
 

You can see that there are a number of holes with town names inscribed next to them. This allowed the user to move the gnomon, and therefore adjust the latitude, depending on where they were situated. This one is set for 51° north, the latitude of London. The time would have been read from the shadow cast by the gnomon on the bottom surface.
 

Above the latitude holes you can see the signs of the zodiac. These were used to indicate the time of year and the length of the day in hours (Quantitas Diei).
 

There is another sundial on the lower surface. It has a tiny gnomon of its own that shows the time according to the old systems of Babylonian (0-24 with 0 at sunrise) and Italian hours (1-24, beginning and ending at sunset).
 

Next to the lower dial is a magnetic compass, used to align the sundial. It shows the four cardinal directions:

Meri - 'Meridies' (midday) Latin for south
Occi - 'Occideus' for west
Sept - 'Septentriones' for north
Orie - 'Oriens' for east.
 

There is another compass on the outer lid of the dial. This would have been used for orienteering.
 

On the underside of the dial is a moondial. The pointer converts the time shown on the main dial if used for the moon at night. The pointer is set to the number of days after the last new moon (outer ring) and the time at night is read off opposite.