created by Carl Sabanski
Diptych Sundial: a portable (pocket) dial in which a vertical and horizontal dial are hinged together, and a common cord gnomon running between them also ensures that they open to the right angle. Latitude specific.
Now that you can design and build horizontal and vertical direct south sundials, you can put them all together to create a portable diptych dial. All you need to do is create two miniature sundials. How small they are will depend upon your skill with the materials you are working with. Figure 1 shows the layout of a diptych sundial.
Figure 1: Diptych Sundial (ZW2000/CAD)
To function, the two sundials must be positioned correctly on the two plates. When the sundial is opened the plates must be at right angles to each other. This is accomplished by using a cord gnomon of a specific length "L". The cord forms the style of the sundials.
First position the horizontal sundial on its plate and measure the distance "H" from the dial origin to the top edge of its plate. The distance "V", from the origin of the vertical sundial to the bottom edge of its plate, can be calculated as follows:
V= H tan ø
where ø is latitude of the location where the sundial will be used.
The vertical sundial can now be positioned correctly on its plate.
The two sundials are now hinged at the base and a small hole is drilled at the origin of each dial. The sundials are opened so they are at right angles to each other. The ends of the cord are passed through the two holes and attached so the cord is tight when the dials are opened to the correct position. This is only one way of attaching the cord.
An option is to attach a plumb line to the vertical sundial to ensure that it is in a vertical position when opened. A bull's eye level can be installed on the horizontal sundial to level the dial.
To read the time the dials must also be aligned with the celestial pole. Dials of this type included a small compass embedded in the horizontal dial.
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