RVR is a critical component in determining what the ILS minimums will be for each landing Category. The RVR equipment are located next to a runway that provide air traffic controllers with a measurement of the visibility at key points along a runway (e.g., touchdown, midpoint, and rollout). The data is used to decide whether it is safe to take off or land during limited visibility conditions. During reduced visibility weather conditions, RVR system measurements are used by air traffic controllers to establish airport operating categories. The RVR reading is key to determining the category of precision approach capability required to conduct safe aircraft operations. These readings also assist Airport Traffic Control (ATC) when issuing control instructions to avoid interfering operations within ILS critical areas at controlled airports. The lowest authorized ILS minimums, with all required ground and airborne systems components operative, are: (a) Category I Decision Height (DH) 200 feet and RVR 2,400 feet (with touchdown zone and centerline lighting, RVR 1,800 feet); (b) Category II DH 100 feet and RVR 1,200 feet; (c) Category IIIa No DH or DH below 100 feet and RVR not less than 700 feet; (d) Category IIIb No DH or DH below 50 feet and RVR less than 700 feet but not less than 150 feet; (e) Category IIIc No DH and no RVR limitation.