This film shows how the makers are trying out the wooden cogwheels of the planetarium. These cogwheels should not shrink or expand due to changes in humidity or temperature. That’s why they choose for pear wood, with its excellent properties in this field. De cogs themselves are made from a rust free copper alloy, they were mounted by hand, one by one. Just like the planetarium of Eise Eisinga in Franeker, the planetarium in Zuylenburgh is driven by weights and regulated by a pendulum. It actually functions as a gigantic pendulum clock, a 17th century invention by the great Dutch physicist Christiaan Huygens.