How many people are in each area

Two lines and three areas are drawn onto the image. The lines go where people really come in and out of the room: the gate at the back and the foot of the staircase. Each line has a direction, so crossing it inwards adds and crossing it outwards subtracts, and that subtraction is how many people are there right now. The areas are painted over what you want measured separately: the room, the upper landing and the ground around the post. None of this is asked for out loud. Asking is for searching and for describing a situation; counting is for measuring, and they are not done the same way: a line cannot be described in a sentence, it has to be traced, because the figure depends on exactly where it runs and in which direction. It is traced once and stays there, so Tuesday's figure and Saturday's are measured the same way. That is what makes the figure repeatable and auditable, and it is why people counting can be type-approved.

This is not attendance control and it does not take a roll call: it does not say who is there, it says how many. The difference matters the day a wing has to be evacuated. Knowing there are thirty-one people inside and believing there are twenty-eight is not a nuance: it is three people nobody is looking for. Today that number comes from counting by eye from the post and checking it afterwards, and minutes go by in between. With the lines and areas in place, the duty governor has each area's count as it stands and the curve for the whole day: what time the room fills up, how far it drops at count time and at meals, how many go up to the landing. That is what it takes to decide how many officers cover Saturday afternoon, and to check a count without arguing about it. The figures on the illustration are an example, not any facility's measurement.