City governments increasingly install sensors that report how long public benches remain occupied. The data seem to offer an objective basis for deciding where more seating is needed. Yet a bench used continuously by one person and a bench used briefly by twenty people may produce the same occupancy total. Unless planners combine duration with turnover and observe who is unable to sit, the metric can make a crowded square look adequately served. The problem is not that measurement is useless, but that a single count may ________.