If the RVR group is reported as R12L/1000V4000FT, what does the portion after the solidus ("/") signify?

The notation R12L/1000V4000FT indicates that the runway visibility range (RVR) for the specified runway (in this case, R12L) is varying between two values. The portion after the solidus ("/"), which shows as "1000V4000FT", means that the RVR is fluctuating and is reported as 1,000 feet at its minimum visibility and can reach up to 4,000 feet at its maximum visibility.

The 'V' in this context signifies "varies", indicating that the RVR is not stable; instead, it is changing within that range. This is an important piece of information for pilots and air traffic control as it affects decision-making regarding landing and takeoff operations.

Understanding this aspect helps in recognizing the operational implications of variable visibility on flight safety and operations at the airport. The other options do not accurately represent the nature of the reported visibility range; they suggest stability or fixed values, which contradicts the indication of variability in the RVR readings.