NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: CP-300/U USAF Star Finder
From: Brad Morris
Date: 2019 Jun 28, 20:40 -0400
From: Brad Morris
Date: 2019 Jun 28, 20:40 -0400
Alan
You wrote
differences between and arguments over which of the two devices is "better or superior"
Ed, in his paper, specifically contrasted the two devices, defining the differences. Either device is well suited for primary purpose, which is to plan a round of sights. Either one will provide sufficient accuracy for this task.
There are two main differences
1) The CP-300/U uses one common base and two additional inset disks which mean you do not have to perform the addition of GHA Aries to your longitude. To obtain LHA Aries, you just move some disks. Its your judgement call if the additional expenditure is worth the addition (pun fully intended). Some could say that the Air Force can't add, so we had to give them a way to avoid it. Others will say that it removes common mistakes in addition so amply demonstrated by the Navy, when using the 2102D.
2) The azimuthal overlays slide in latitude adjustment, providing a different answer. Notice I did not say more correct answer or less correct answer. The azimuthal equidistant shape changes as a function of latitude. Consequently, this provides ZERO advantage for additional cost, simply because the shape on the overlay does not change. An easy way to illustrate this is to assume you are at precisely 30° latitude. You may then select either the 25° overlay or the 35° overlay, moving them the 5° necessary to get to 30°. Yet the two overlays have different shapes!! So it is clear that the shape should be somewhere in between.
There is no doubt that the "enhancements" of the CP-300/U are more costly. They also make it more fragile. My preference therefore is the 2102D. Your milage may vary. As stated earlier, either one will provide simple effective planning. The answers will be approximately the same, which will be good enough to put the star in your telescope.
Brad
On Wed, Jun 26, 2019, 7:47 PM Alan S <NoReply_AlanS@fer3.com> wrote:
Digging around in what might well be ancient history, the differences between and arguments over which of the two devices is "better or superior" begins to sound like mine is bigger than yours, not that it makes any real difference.
