[In principle, in system geometries where there is local field-enhancing nanostructure present, and the macroscopic conversion factor β M can be determined, knowledge of β then allows the value of the emitter's effective field enhancement factor γ to be determined from the formula γ = β / β M. In the common case of a film emitter generated on one plate of a two-plate arrangement with plate-separation W (so β M = 1/ W) then