hehehehe, it's Nikoneese David.
In the 60's the first Nikon F-mount lenses used a "fork" metal thingies that look like rabbit ears to "set or calibrate" the internal meter to the lenses f-stop settings.
In the late 70's Nikon changed the meter system a little tab or ridge on the side of the lens near the mount that does the same thing but is much smaller and less noticeable and it is called the AI-s Automatic Indexing system.
When the AF lenses came out this information started to be transmitted through the electronics but the new lenses (except for the G lenses) still have the AI-s tabs.
Also, Nikon lenses are still made with the slot and screw guides to put the "forks" on them(except for the G lenses) This literally means that I can put a Nikon lens made in 60's onto a D1 and it will meter correctly if it has an AI-s conversion kit installed on it. [img]/ubbthreads/images/graemlins/wink.gif[/img]