BC Gnomonics
Vetus Quadrant /
Quadrans Vetus /
Unequal Hour Quadrant
Universal, Altitude, Seasonal hours
This sundial quadrant continues to go by its latin name, quadrans vetus, or "old quadrant," after the system of season hours it uses to reckon time. The dial is also often referred to as the vetus quadrant, which is simply an evolution of the pure latin.
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The dial is effectively universal, able to be used so long as the operator knows the degree height of the sun at noon for the day of operation. This value can be found using another instrument, in an almanac, or in some cases, on the dial itself.
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In certain historical examples, the quadrant contains a latitude-specific table of values to tell the user how high the sun culminates for every day of the year.
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Like many other portable dials, the vetus quadrant is known to be made from wood, ivory, or various metals.
How to use
1. For dials with only hour lines and a degree scale:
Tilt the quadrant back until the thread falls on the altitude scale at the sun's highest degree for the day of operation.
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For dials with a sliding date scale:
Slide the date scale so that its center aligns with the colatitude of the user's location (90º - your latitude).
1b. lay the thread over the current date. When the plumb bob hangs with the dial inclined to this degree, the quadrant will point to the noon sun for that day.
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2. With the string fixed at the sun's culminating degree for the day, slide the bead to the line of the 6th hour.
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3. Tilt the dial until the sun's rays pass directly through both sights. This can be done by aligning the shadow of the first sight's hole with the hole of the second.
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4. Note where the bead falls on the hour scale. The segment in which it falls indicates the current seasonal hour.
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