This 17th-century boxwood English nocturnal has pointers for both the Great and the Little Bear constellations. Some nocturnals had pointers only for one of the bears.
A nocturnal is a device for telling the time by the stars. It could be accurate to about 15 minutes. They were popular from around the 15th to the 17th century, with a few being made into the 18th century.
How to use a English boxwood nocturnal:
• Set the long pointer to the correct date (the outer scale)
• Hold the instrument by the handle at arms length.
• Look through the hole at the centre at the Pole Star
• Once in position, move the two short pointers labelled 'LB' for Little Bear and 'GB' from Great Bear until they are lined up with their appropriate constellations.
• As the pointers LB and GL move, so does the time scale.
• Where this scale crosses the long pointer read off the time On the backside one can find the regiment of the polestar, as in this period the polstar had a distance of 2,6° from the North Celestrial pole