The question you asked is very simple. The reason is that the water meter of each unit is connected from the first floor. Since the pipes are thin, if the users on the lower floors release water, it will affect the water in the pipes of the unit. pressure, causing the water in the pipeline to fluctuate, causing the water meter to rotate slightly. I wonder if you have noticed that the slight rotation of the meter needle sometimes rotates in the opposite direction, and sometimes in the forward direction. If it always rotates in the forward direction, then this watch is anti-reverse. If so, Users suffer.