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Preparing the sundial

Choose a site for your sundial that is in sunlight for a large part of the day. The dial should be flat, but it can have any orientation, and it can be horizontal, vertical, or even sloping.

On the flat surface, draw a square or a rectangle of the size you want to give your sundial. Make sure that the corners are right angles: exactly 90°.

Select the side you will call "top". For a vertical or slanting sundial, the choice is obvious, but you also need to make this assignment for horizontal sundials. When Calcad produces the diagram of the sundial, it will represent the "top" side ... at the top!

Draw two straight lines between the centers of the opposite sides to get the center O of the square or rectangle. The straight line that connects the left and right sides will be the x axis X'X, the other one will be the y axis Y'Y, with Y on the "top" edge. This axis system will allow you to note the position of any point inside the dial.

Install a temporary gnomon, with its tip above point O (perpendicular to the plane of the dial), at a distance that is about a quarter of the shortest side of the sundial. You will measure the position of the tip's shadow on two separate occasions to provide Calcad with the information it needs to calculate the layout of the dial.

Check the perpendicularity by set square (photo 1). Do this at least twice, with the set square aligned in different directions.

Measure the height of the tip accurately (photo 2).

Photo 1Photo 2

Now you can specify the dial information for Calcad. Open the input box by clicking on the Input menu or by typing 'Escape' on the keyboard, then enter the side of the square (or the height and width of the rectangle) and the height of the gnomon's tip.

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