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Farmer's Ring /
Ring Dial /
Altitude Ring Dial

Latitude specific, Altitude

Traditionally made from either wood or metal, the farmer's ring is perhaps the simplest altitude dial to use. In use, the ring's nodus allows a beam of sunlight to shine on the inner hour scale of the ring. Some dials of this type are equipped with a seperate fixed nodus for the summer and winter months, while others feature a single sliding nodus that can be set the the moth of use.

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History of Science Museum

How to use

1. If the dial features a sliding nodus, shift the nodus to the current month.

2. Suspend the dial and rotate it until a beam of light is projected through the nodus onto the hour scale.

3. Twist the dial so that the spot of light lies on the center line of the inner scale.

4. Read the time, making sure to read the half of the hour scale corresponding to the correct side of noon.

5. To determine civil time, add the appropriate longitude correction and equation of time correction (more information here). If applicable, add one hour during daylight saving time.

Overview of Instrument
Outdoor Demonstration
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