BC Gnomonics
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.
History of Science Museum
Helmut Sonderegger
Nicolas Bion
How to use
1. If the dial features a sliding nodus, shift the nodus to the current month.
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2. Suspend the dial and rotate it until a beam of light is projected through the nodus onto the hour scale.
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3. Twist the dial so that the spot of light lies on the center line of the inner scale.
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4. Read the time, making sure to read the half of the hour scale corresponding to the correct side of noon.
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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.
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