What does "RVR 24 or 1/2" mean at this ILS chart?

Question

runway visual range 24=2400 ft?, or 240 ft?, or 24 meters?? and for what does the 1/2 stand?

http://i213.photobucket.com/albums/cc115/PilotFerdi/ajfk.jpg

Answer 1

rvr,or Runway Visual Range is reported in hundreds of feet (in the US) in this case it is 2400' ,1/2 is 1/2mile

Answer 2

RVR = Runway Visual Range  and the 24 is indeed for 2400' and the 1/2 means  1/2 statue mile visibility. This is most common on a standard Cat I ILS visibility Minimum.  The RVR is measured by a transmissometer which determines how far it can "see" in hundreds of feet. If there is one installed on the runway you are approaching, and it is working, then it is controlling and the tower will reference the current vis from it. If it is not working, or if you are landing on another runway not served by the system.. then the tower will call the visibility to the best he can see. So.. if he can see old man Johnson's barn which is 3/4 mile away.. then he can call it 3/4 mile. If he can see the blue taxi lights on the far edge of the ramp that is 1/2 mile away... you get the idea.

RVR can be a basic system on the end of a runway, or it can be a more advanced version with multiple stations that can measure the touchdown area, the midfield and the rollout.

The common joke among pilots in the holding pattern waiting for the vis to come up to the minimum to land and it isn't moving around any at all.. is to tell the guy on ground to go out on the field and get the possum out of the way so RVR will read properly.