Tide abacus key ring
REF: H93 Tide Abacus Key Ring
It is a replica of the Nocturnal Nocturnal and Tide Abacus of 1570, signed by Humphrey Cole. This instrument is currently in the British Museum, London. One of its faces is this abacus or tide computer and the other is a Nocturnal.
The abacus or tide computer is used to calculate the times of the tides. The tides with their constant change of the water level have effects of great importance for navigation, for harbours and for fishing.
Diameter: 50mm / Thickness: 6mm