Not long after the invention of the sundial, someone came up with the idea of making one that could be carried with you. But it was soon noticed that the further you travelled north or south, the more inaccurate such devices became - the reason being that the apparent height of the sun varies with latitude. For a portable sundial then, the angle of the gnomon (shadow striker) has to be adjustable for different locations. This universal ring sunwatch, based on a popular 16th century design, allows compensation for latitude and time of year (a further refinement) and also folds flat for carrying. It is precision engineered in solid brass and offers a fascinating insight into the history of timekeeping. Diameter 2.5".