The universal ring dial was the answer to telling time at sea during the day. They were most popular from the 1600s through the 1800s. Unlike sundials which used flat disks, the universal ring dial can be used anywhere in the world and is self correcting. When held by its upper ring, it would stay steady when used on small ocean swells thereby allowing accurate readings on a rolling and pitching ship. Their normal size was about 12" in diameter and could be folded up for safe storage. Used in conjunction with a nocturnal, you were able to achieve accurate time almost 24 hours a day.
Even the invention of the mechanical clock did not make the sundial obsolete. In fact, the early clocks were regularly calibrated with sundial readings. In the late 1800s is when reliable chronometers were manufactured and the sun dial would begin to loose ground. However, sundials were still in regular use into the early 1900s for calibration of clocks and still used for navigation.
This coin is currently in prototype stage. You can make other navigation coin purchases at the CoinsAndPins.com Navigation Geocoins page.