The ascending passage is formed from similar geometry constructions to those used on the previous pages. The ellipse that is highlighted on the drawing is a copy of the principal ellipse, a polar cross section of the Earth, and is inscribed within the two faces and base line of the pyramid. The method of constructing of the ascending passage in the geometry is first to inscribe the ellipse inside these three tangent lines (mouse over the elements to highlight them)
When this construction is performed it creates three tangent points on the three lines. Using these points the ascending passage is formed as follows :
If you open the object information panel for the ascending passage line you will see that the angle from the geometric construction is 26° 1' 34.01" and that it varies from that of the surveyed value by 0° 5' 6.02" which is well outside the surveying error margins.