Vibrations from the floor must not propagate to the telescope. Therefore, the concrete footing does not touch the floor, joists or battens. The pyramid-shaped footing is in contact only with the bedrock and the compacted gravel layer over the bedrock.
Together with the radial pattern of the floorboards, this complicates the layout of the floor joists. The joists can only be in contact with the cylindrical wall and the underlying compacted gravel.
The finished floor is located in the same plane as the top of the pier footing, forty centimeters above the gravel layer. The battens are 2x6” and joists are 2x8”. This is very oversized relative to the span between joists. The reason for using over-dimensioned lumber is that this combination puts the floorboards at precisely the correct height.