The video on the left is comprised of 17 frames between Zapruder 183 and 206. Some frames were omitted due to blurring but consecutive frames were never omitted so there are still some blurry frames. The timing was adjusted accordingly. Phil Willis seemed to be telling the Warren Commission that his startle reaction to the first shot made him snap the shutter on the fifth slide he took in Dealey Plaza. He said, "Then my next shot was taken at the very-in fact, the shot caused me to squeeze the camera shutter, and I got a picture of the President as he was hit with the first shot." His then ten year old daughter Rosemary said she stopped when she heard the first shot. Gerald Posner and many others have interpreted this to mean, "I was running and did not slow down one bit until I heard a shot." Stopping when she heard the shot does not imply that she could not have already been slowing down. It appears that her last step had ended by about to 0.3 seconds before she turns but her arms are still swinging. Allowing for reaction time, the sound would have reached her 0.1-0.2 seconds after her last foot went down and maybe before. Phil Willis is the best witness for the timing of the first shot and is perhaps the best that could be hoped for. He describes a reaction to the shot that would happen very quickly and that we can unambiguously interpret. He snapped the shutter and we can accurately place his action in the Zapruder film. He may have been wrong about his startle reaction causing him to snap the shutter , but if Rosemary's slowing down is a reaction to the shot, then the shot came two seconds before Phil took his photo and about a second before he lifted the camera to take it. It is hard to imagine that he was that far wrong. As the limo made the turn on to Elm street it was moving slowly and Rosemary had the inside on the turn. She was running right beside the limo. By Zapruder 183, JFK is about 30 feet down the road from her. Perhaps she didn't really decide to stop but gave up on chasing the limo and a slow, gentle autopilot stop followed. More video of Rosemary Willis. WARNING. Possibly annoying audio.,
As explained here, the red line represents a vertical plane between Willis' and Zapruder's cameras. In order to determine to which frame the Willis slide most nearly corresponds, a true vertical line must also be drawn from Willis' camera in the Zapruder frames. The Zapruder frames are transformed so that they are as they would be if the camera were pointed as it is in 206 with the camera leveled. From the camera direction, the long north- south wall should have a slope of 0.01 degrees. This was used to level the camera.