Step 4: Fold and Glue the Gnomon
Make all the creases in this step nice and sharp. It will be difficult to keep them sharp as you reach the end where they come together. Using a ruler may be helpful.
Start by folding the gnomon in half along the central mountain-fold line, and pressing the halves together (photo 1). Make the halves line up nicely.
Then fold back (in the opposite direction to the first fold) along the next two lines, which are valley-fold (photo 2).
Next, carefully glue together the two triangles on either side of the central mountain-fold line, up to the valley-folds you just did (photo 3). Don't use too much glue--you want a very flat and straight joint. Wait for the glue to set a bit before the next step. If you want the gnomon to be stronger, you can embed a wire extracted from a wire-tie along the crease.
Finally, you have two small flaps which will be used to glue the gnomon to the triangular (or, more precisely, diamond-shaped) area on the dial. They are attached with mountain folds--crease them so they join up but do not overlap (photo 4).