This time lapse movie was taken over the course of about 7 hours. You can tell the direction of the sun by the shadow the heliostat casts on the grass. It is aimed at a 2' x 2' white-board 120' away. Over time the focal point drifts slightly to the left side of the target. This represents about 1 degree of mechanical calibration error. Just over halfway through the movie you will see that I set the focal point back to the center of the target. If you step through this movie frame by frame you can see the focal point drift when the clouds obscure the sun. The shadows of the trees late in the day also cause the focal point to drift.