[Duke 13370]

The way a normal grandfather clock works would work for the task, but it takes time to create and test. Basically, there would be a large pendulum that swings back and forth (probably once every other second). when it swings in one direction, it trips a lever, advancing some sort of counting mechanism (like spinning an arm X degrees or pushing a beam X cm).

or, you could just build a pendulum and count the swings yourself if it's allowed.