In addition to the eight positions shown above you may want to add one more roll angle at each position bringing the total to 12 photos. These four additional photographs ensure a better coverage and a complete set of roll angles. While they are not necessary, if you are striving for the highest accuracy you may wish to take them. They are shown below in Position 1 - Roll 90 degrees ccw, Position 2 - Roll 90 degrees ccw, Position 3 - Roll 90 degrees cw, and Position 4 - Roll 90 degrees cw.