AMTG Virtual Cross Staff & Back Staff GC

Help to guide you to another cache. This is a depiction of a device that was used to guide those in the past to their "caches". I love it and want to share it with other cachers.

Large coin with lots of heft. Unusual shape due to the unusual rim work. The front has very nice background texture and rim design. The 3-D work in the medallion is life like, bold and very detailed. It shows small details as well as having raised images. Some of the best 3-D work I have seen. The medallion has raised script that says "Back Staff". The bottom of the medallion image has a copyright symbol and "ACP". The reverse continues the excellent 3-D work. It goes as far as showing a far off ship on the water. The raised script in the medallion says "Cross Staff". Go to www.compassrosegeocoin.com/crossbackstaff.php for information on how it works. Excellent show coin. -------------------coin info: Navigation: The Cross Staff and the Back Staff: The cross-staff consisted of a long staff with a perpendicular vane which slides back and forth upon it. The staff is marked with graduated measurements -- calculated by trigonometry. The angles can then be measured by holding it so the ends of the vane are level with the points to be measured. Early in the sixteenth century it was already in use as a seaman's navigational instrument. Originally the staff had only one vane and was very long. Therefore, it was very difficult to manage on a rocking ship. The mariners added more vanes in order to reduce the length of the staff to about 2 1/2 feet. The long, medium and short vanes on the staff were about 15, 10 and 6 inches in length. The staff was then calibrated directly into degrees for use on board a ship. For the most part, the cross-staff was used to find the latitude by measuring the altitude of the Pole Star above the horizon. This, of course, was useless in cloudy weather. It could also be used to determine the altitude of the sun, but this required the observer to look directly into the blinding sun. In the early seventeenth century, the back-staff was developed to avoid this problem. It would not be practical to make a cross-staff because of its length and detail. However, the teacher might want to include the worksheet as a coloring page to be added to the pupils' notebooks. Early in the sixteenth century it was already in use as a seaman's navigational instrument. It was introduced into England in the mid-sixteenth century, where it was further developed to measure the angles between stars, and to measure the heights of buildings or topographical features such as mountains and hills. A very early navigational instrument, the cross staff was widely used among surveyors and astronomers. It was not until the 1500s after it was developed further that it started to be used at sea. The name is derived from its cross shape. It was cumbersome to use simply because a user had to focus on the horizon and star or sun at the same time; moving your eyes from one to the other and at the same time sliding the transversal (cross piece) until you achieved what you thought would be an accurate reading. It also required looking straight into the sun when taking daytime readings. It was with the invention of the back staff that these problems would be resolved. John Davis invented a back staff in 1595 and his improved design became known as the Davis Quadrant. It rendered the cross staff obsolete since the user only had to take a sight at one object and didn't have to look at the sun to take a reading. Appropriately named, its basic design is like a cross staff, but with some enhancements. Daylight readings were taken by having your back towards the sun. In many cases, John Davis's invention ended up replacing not only the cross staff, but also the mariner's astrolabe and quadrant. It was in the late 1700s when the octant and sextant became the new preferred tools over the back staff. ------------------------------------------------------ So many of my trackables have been muggled that I release new GCs as virtuals. If you do not approve, please leave it in the cache for a cacher who understands. Thanks. BL