NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Another "emergency navigation" sight reductionmethod
From: Stan K
Date: 2015 Jul 8, 09:47 -0400
From: Stan K
Date: 2015 Jul 8, 09:47 -0400
Hanno,
Recent exam grading experience is beginning to convince me that there will never be the "perfect" longhand sight reduction method. Maybe a sign of the times, but it seems that some people cannot even add or subtract when they have a calculator available.
The hav-Doniol calculation of Z, with its division, is out of the question, but the Azimuth Graph provides an alternative. The hav-Doniol calculation of Hc has its sore point, its single multiplication. But every method requires addition and subtraction, and, from what I've seen recently, either the American education system is going to hell or people are just too lazy to check their work.
I'm probably just blowing off steam. When grading these exams we allow for "dependent errors", where there is no deduction for subsequent errors that are based on a previous error, if the subsequent work is done correctly. Having a little math error makes me have to check every calculation of every subsequent step, both time-consuming and frustrating.
Getting back on track, I have been thinking about the wants and needs of USPS students vs. real emergency navigation use. I have to assume some competence in basic mathematics, or at least in the use of a calculator. What I think it comes down to is the comfort zone of the user. Any of the methods discussed (even NASR as an emergency navigation method, IMHO) becomes fairly easy with enough practice. We do man overboard drills, so why not practice emergency sight reduction?
Stan
-----Original Message-----
From: Hanno Ix <NoReply_HannoIx@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Tue, Jul 7, 2015 6:57 pm
Subject: [NavList] Re: Another "emergency navigation" sight reductionmethod
Greg Rudzinski has made experiments a couple of days ago with
an hav(x) table with 10' steps and 4 digits entries and good results.
You might want to take a look at them. It might well be an advantageous
alternative to N(x).
True, hav - Doniol does not as easily deliver the azimuth as N(x) / NN(x) do.
From: Hanno Ix <NoReply_HannoIx@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Tue, Jul 7, 2015 6:57 pm
Subject: [NavList] Re: Another "emergency navigation" sight reductionmethod
Stan,
back again. And I agree, scaling as described has certainly
advantages for many tables, not just N(x).
You might want to take a look at them. It might well be an advantageous
alternative to N(x).
hav-Doniol delivers Hc fast, cleanly and accurately for all combinations
of L, d and t because it is mathematically a strict calculation, Opposed to that,
Ageton, Dreisenstock and N(x) / NN(x) have limitations here as
I pointed out before. I presume that could become a problem in an
I pointed out before. I presume that could become a problem in an
emergency package when they are the sole SR method available.
True, hav - Doniol does not as easily deliver the azimuth as N(x) / NN(x) do.
But the azimuth diagram that we recommend does. This diagram is
actually a graphical means to calculate the product sin(x)* sin(x) and
sin(x)*cos(x) and therefor useful quite a bit beyond azimuth calculations.
Sun rise / set and identification of a body are just 2 of them. For this reason
it has its own stand-alone value.
So, perhaps these additional capabilities justify its inclusion into an emergency
package anyway and thus it bypasses the azimuth calculation a la Lars Bergman.
H
On Tue, Jul 7, 2015 at 11:11 AM, Stan K
<NoReply_StanK@fer3.com> wrote:
Hanno,
I saw the message about the NN(x) Table, but I didn't give it much thought because it would not be recognizable as David's N(x) Table. Perhaps not a good reason, but, as you said, you did not pursue the idea because, in effect, you end up with the equivalent of Ageton. It would not be much different than comparing Mike Pepperday's and Rodger Farley's S-Tables. But now the idea intrigues me, so I might just take a closer look. So what if it no longer has the same entries as the N(x) Table.
Stan
-----Original Message-----
From: Hanno Ix <NoReply_HannoIx@fer3.com>
To: slk1000 <slk1000---.com>
Sent: Mon, Jul 6, 2015 11:42 pm
Subject: [NavList] Re: Another "emergency navigation" sight reduction method
N(x) is actually an logarithm of something. Assuming you are always using the same table the absolute value of the entries in a log table are irrelevant - only their ratios matter. So if you where to divide your table by the maximum value - here 5840, actually 0.5440 - then the biggest number would become 1.0000 or, written w/o period, 10000. The other values would grow in the same ratio.The biggest number on your table is 5840. So, there are just 5841 numbers available for the entire table which means the resolution is 1 out of 5841 incl. 0, correct?Stan,let me repeat an observation and then an idea.
If you continue using just 4 digits again (except for the entry 10000 itself) all of a sudden you get a resolution 1 out of 10000 out of the 4 digits. Therefore, you practically doubled the available resolution and, accordingly, reduced any rounding errors by abt. 50%. This is significant particularly for the very small entries.
So, the idea now is doing just that: divide all entries by the biggest entry, and you will exhaust the entire number space available therefore minimizing possible rounding errors. Again, that number space when 4 digits are used is now 0 to 9999 in steps of 1.
D.. Burch could have used with advantage that scaling for his original N(x) .
Only if you are concerned about communicating the logarithms per se and not the corresponding natural value to somebody else there would be a problem, and you would also have to communicate the type of scaling you did. This is never a problem when you do SR with the same scaled log table.
BTW: the way such scaling is communicated is by mentioning the base of the logarithm like 2, e, or 10 which are actually being used in technology. Here you don't even have to know that.
I hope I was able to describe this in understandable terms.
H
On Mon, Jul 6, 2015 at 4:06 PM, Stan K <NoReply_StanK@fer3.com> wrote:
FWIW, attached is an N(x) Table with 10' increments, using Hanno's format. It is barely over a half a page as is, but could be made smaller by not having three columns of minutes and by eliminating the 60' lines completely.
StanAttached File: 132099.n(x)-10-90d.xls (no preview available)
