Though image-intensification technology employed by different manufacturers varies, from the tactical point of view, a night-vision system is an optical device that enables vision at low light. The US government itself has recognized the fact that technology itself makes little difference, as long as an operator can see clearly at night. Consequently, the United States bases export regulations not on the generations, but on a calculated factor called "figure of merit" (FOM). The method of FOM calculation and its implications for export are briefly described in a National Defense University document called “The NATO Response Force” authored by Jeffrey P. Bialos, the Executive Director of the Transatlantic Security and Industry Program at the Johns Hopkins University, and Stuart L. Koehl, a Fellow at the Center for Transatlantic Relations of the same university.