By having a better understanding of the criteria needed for Category I operations we not only aim for an improvement in safety in Category I operations but we can move off from a more rational basis into Category II. In any case the dividing line between Category I and Category II, that is 200-ft. decision height and 800 m. RVR is not very well chosen as far as the RVR quantity is concerned and in the U.K. we generally refer to Category II as meaning a lowering of the decision height as airlines have been using lower RVR minima than 800 m. for a number of years. With the final part of the approach still having to be made visually, the main instrument approach criteria with which we are concerned are the weather minima—the critical height or decision height and the RVR or Met. visibility.