In order to improve stability, I reduced the number of panels from five to four. A pleasant surprise was that the removal of the central back panel not only resulted in a more compact and stable cooker, but also improved the efficiency of the reflective surfaces, by permitting multiple reflections between the two remaining vertical panels. Fold down the front panel ABCD using BC as a hinge. Cut and fold another piece of cardboard so that it can be inserted into the box to form panels 1 and 2 in figure 3. The angle formed by these panels is adjustable at time of construction.
Smaller angles concentrate the sun more, but require more frequent adjustment to follow the sun.
A good compromise seems to be any angle between 60 and 90 degrees. Cover this piece with aluminum foil and glue or staple it in place. Apply aluminum foil to panels 3 and 4 as well. These dimensions correspond to a reflective area of about 5,000 sq. The single notch near panel 4 is used to lock this panel in a closed position for storage.