The drawing shows the unrotated secondary ellipse and the lower southern shaft geometry line both highlighted in green, and the object information panel shows the angle of the lower southern shaft of 39.52517°. The length of the shaft line from the tangent point on the ellipse to the end of the shaft is 221 times its angle in radians.
The angle of the geometric shaft line can be adjusted by rotating the secondary Earth ellipse to its naturally occurring and known fixed axial tilt, in an identical manner to that which was performed to create the ascending passage's correct construction angle.
Keep your eye on the lower southern shaft angle in the object information panel and click here to apply the axial tilt to the secondary ellipse. When this rotation is applied to the ellipse the angle of the geometric construction line changes to 39.5870° and varies from that of the surveyed value of the shaft's angle by two hundredths of a degree, which is well within the tolerances of the digital inclinometers and statistical analysis of the robotics surveying team.