you can go because 6/6/m is ok, you can have one missing. They are light guns, that shoot down the runway and with a fancy computer inside they measure how far they can "see", which is converted to human talk and gives you the distance you can see from the cockpit while looking down the runway. I am trying to keep this simple. The chart put out by the FAA/airport tells you what is legal for take off at that airport/ runway from those light guns. If one light gun is broken and the report is missing you can take off, if two are broken can NOT go. However you can never ever go if they fall below what the chart says is legal. The chart will also say that those bright lights all over the runway you can see have to be working, and if some are not working then the RVR becomes a higher value since you have less to see from the cockpit around you to tell where you are going.

Now to try and put this on an understandable level, lets just say that you have 3 RVR guns at somewhere like San Francisco which is on a bay next to water, and two guns are on the runway away from the water, and one rvr gun is right next to the water, somewhere that would typically get much thicker fog. Rumor has it that ATC might say the RVR is 6/6/m to keep traffic moving since that 3rd gun is not really realistic to the remainder of the airport, due to its close proximity to the water. Thus if ATC were to report 6/6/5 the airport would come to a standstill, so something like 6/6/m would keep things moving. !!!!!Now that is merely a way to remember it and not how things would ever really work in real life.!!!!



Is there someone who really into being a CFII on here that wants to explain it quoting the AIM/FARs and give a better answer.