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Cross Staff & Back staff Geocoin
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.
|Size||30 - 45 mm|
With each travelbug, travel tag, geocoin of other trackable, you need an activeringscode to activate your trackable at Geocaching.com.
Sometimes, the code is already added, e.g. with most travelbugs. It is then available at the paper card which is included with the product.
With the other trackables, you need to request the activastioncode at our website via the following link:
Sorry, no that is not possible.
You can use your own code on certain products.
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No, with most trackables, a code is already placed on the product in the factory (travel bugs, geocoins, travel tags, etc). For some products (eg the personal tag or stickers) you can specify a code that you already have from another Geocaching product. Or if you want a sticker made with an existing code.
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