This video is a working clock. We see two men filmed from above sweeping rubbish in an otherwise vacant space. They are marking time by pushing two long piles of trash around with their brooms, with one pile advancing precisely every minute, and the other every hour. Their actions were filmed for twelve hours, which is also the length of this video – exactly one-half day. Dutch designer Maarten Baas has created several other clocks like Sweeper’s Clock, in which the passage of time is marked by human actions.