Hemisferium Lunar Calendar & Tidal AbacusThis beautiful replica consists of a Perpetual Moon phases calendar on the front face and a Tidal Abacus or computer on the back. This instrument was conceived to address the need to predict the time of tidal changes. It draws on the intimate of the Moon and the Earth which influences the tides. Knowledge of the lunar phases has been of great importance for many cultures calendars, religious festivals, and agricultural practices were all set according