The code that deals with particle transport within the PMT and reflector assembly uses a coordinate system based on the PMT with the Z axis aligned along the PMT's axis of symmetry. The mapping between detector coordinates and this system is performed by the routines GEH_MAP_DIRECTION and GE_MAP_POINT. This mapping is inadequate because an arbitrary assumption is made about the rotation around this axis . Note that only the petals break the rotation symmetry so this assumption is acceptable so long as the exact petal orientation is undetectable.