NOTES TO OFFICIAL USERS
			
						
									
              Air Ministry Orders and Vol. II leaflets as issued from
         time to time may affect the subject matter of this publication.
         It should be understood that amendment lists are not always
         issued to bring the publication into line with the orders or
         leaflets and it is for holders of this book to arrange the
         necessary link-up.

              Where an order or leaflet contradicts any portion of this
         publication, an amendment list will generally be issued, but
         when this is not done, the order or leaflet must be taken as
         the overriding authority.
              
              Where amendment action has taken place, the number of the
         amendment list concerned will be found at the top of each page
         affected, and amendments of technical importance will be
         indicated by a vertical line on the left-hand side of the text
         against the matter amended or added.   Vertical lines relating
         to previous amendments to a page are not repeated.  If complete
         revision of any division of the book (e.g. a Chapter) is made
         this will be indicated in the title page for that division and
         the vertical lines will not be employed.