The machinist flattened the 10 mm thick sheet metal by applying six thousand kilograms of pressure across rollers 15 cm apart. Several passes and a lot of eyeballing made the quarter segment of the rotation ring flat.
Before bolting, the diameter of the ring was adjusted to 350 cm, with a margin of error of only one millimeter in all directions. This ensures that the upper ring will rotate freely, without being squeezed by the horizontal side rollers.
The fine adjustments of the observatory crown are finally complete. The surface is very level with very few irregularities. Two hundred point measurements with a laser indicate a surface accuracy of 0.5 mm.