The image of the navigator on the front of the Mariner's Astrolabe Geocoin shows how this tool was used when taking a reading from the sun. This Geocoin also has an incorporated raised metal edge around the coin. A real antique mariner's astrolabe would not have this raised edge, but we thought it was important to provide some protection to the spinning alidade. Instead of attaching a large metal ring for the handle, which were typical of old style astrolabes, we attached a rotating clip to make it easier for hooking the astrolabe to a stable item such as a post when taking a reading. The two holes on the spinning alidade are small enough to get a fairly precise reading from sunlight, but are large enough to see through when taking a reading of the North Star, Polaris.