Note key phrases like ". The flight service says its count is accurate within a range of plus or minus 10 percent. " and "This is the first time the firm has used its equipment for crowd estimation. "

Note "This verifiable technique" and "Overlaying the photographs with a grid, surveyors from Air Flight Service estimated crowd density in the plaza and along the route. "

Note "Police and event organizers, when told of The Chronicle's numbers, stood by their estimates of 200,000 marchers, though both groups based their figures almost entirely on observational methods and not on a verifiable methodology. "

Actually count all the little heads and then it will be a "verfiable methodology".

Cheers,
Tony