The interactive drawing shows the same plot as on the previous page (page E1), with the clock automatically started.
If only the yellow part of the dynamic projection is considered, because this is the portion which is explicitly marked off in the architecture with a length which can be calculated from the geometry, and the movement of the projection point is taken as representing the movement of the Earth towards and away from the Sun during its annual orbit, then the two end points of this part of the projection line must represent Perihelion and Aphelion, the two places on the Earth's elliptical orbit where the planet is at its nearest and furthest distance from the Sun. (See the astronomy primer for an explanation of these terms.)
Starting from this premise, we know from the analysis of the measuring stones on the previous page (page E1) the exact length of this plot line, and we also know the real world values of Aphelion and Perihelion from our accurate modern measurements of the Earth's orbit. It must be possible, therefore, to calculate how far away the Sun should be along the slope of the gallery from the plot line end points if the plot is considered to be a scale model. The calculation is as follows:
The measuring stones position the Sun exactly 200 cubits away from the upper end of the yellow dynamic plot line along the slope of the gallery floor, the angle of which is calculated using the 200 cubits to 1 radian length to angle ratio.