Firstly the moon orbits in a synodic period of 29.524 days (0.03% error). Secondly the moon follows an incline plane of 5 degrees. Thirdly the incline plane that represents the lunar orbit precesses over time. A full revolution takes 18.6 years (0.05% error).
The combination of the three movements listed above help to demonstrate why eclipses occur and why they do not occur each month. The brass inclined plate has been engraved with the ascending and descending nodes at the point were the lunar orbit matches the ecliptic.