A simple pinhole. For more complex geometries, :ref:`NXaperture` should be used. Points to the path of the last element in the geometry chain that places this object in space. When followed through that chain is supposed to end at an element depending on "." i.e. the origin of the coordinate system. If desired the location of the slit can also be described relative to an NXbeam, which will allow a simple description of a non-centred pinhole. Size of the circular hole defining the transmitted beam size.