It is certain that the first shot was at about Z123.
In the simultaneous synchronized footage JFK is shown say 10 ft past the signal arm when the first shot happens.
I prefer that JFK is in line with the arm, which is why i deduct 10 frames from Z133 based on 1 ft per frame.
And as a part of that i place Z133 at the point where the sound of the shot has been inserted, not a half second further down Elm.
But the underlying info that i base all of that on might be in error.
I like the analysis of the delays in perception etc, but i feel that an analysis dealing with the earliest reaction rather than a group average would yield an earlier time for shot-1, nearer my Z123, or even say Z113.
Nearly forgot. The CIA footage looking back at the SN shows a large hole in the signal backboard, which is due to the design/manufacture, but i see a small (bullet) hole next to that hole. However for that corner of the signal to get in the way of Oswald's shot the limo would have to be partly into the left lane. I reckon that there was a multi ricochet involving the pipe & collar & guy rods (& perhaps lastly off the signal), the lead hitting the road & 2 copper fragments finishing in the limo, one ovem glancing JFK's head. Hence i am not going to waste time looking for that bullet hole, although if that bullet then ricocheted off the main body of the signal then that could send the lead towards the road & 2 copper fragment towards the limo.