Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    Name or NavList Code:
    Email:
       
    Reply
    Re: Shooting Mercury, Slide rule
    From: Hanno Ix
    Date: 2013 May 30, 21:17 -0700
    Rommel:
     
    Perhaps, I can add my own observations of slide rules as applied in CelNav.
      
    First, the resolution (0.1%) of standard slide rules is just not sufficient for accurate work.
    For estimations and for CelNav in the air, however, they will work. 

    The slide rule also suffers from all log methods, of which it is one: values very big or close to 
    zero - e.g tan(0) or tan(90) - and negative numbers create quite some difficulties, to say the least. 
    Bygrave-like slide rules which are designed exclusively for CelNav can be made to work, though.
    However, you need to observe some special rules occasionally. G. LaPook of this group has championed
    his flat Bygrave, a thing very much worth studying.
      
    Second: Other than the Bygrave I have yet to see a slide rule that has a trig scale on the stock AND
    one on the slide if there is one. The typical slide rules that have trig scales are cumbersome to use.
    An example: cos(alpha)*sin(beta) which occurs in CelNav. You start by looking up cos(alpha) and read the corresponding x. You write it down. Then you look up sin(beta)  and read its x value. Finally, you multiply both values of x to get the result. Never mind that many slide rules have split scales for trig functions,
    one for small angles the other for big ones. So, cos(alpha)*sin(beta) can end up being a complicated procedure on the slide rule, too. The thing gets worse when you need asin(cos(alpha)*sin(beta))!

    If you had a cos scale on the stock and a sine scale on the slider you'd find cos(alpha) on the stock, 
    then sin(beta) on the slider. The rest is standard multiplication; you would at least not need taking notes. 

    Today I am actually at the point where I question the usefulness of logarithms in CelNav altogether. My simulations show that 4 digits for trig functions yield reliably errors less than 1 arc min. However, multiplications of 2 four digit numbers are readily done by hand. The only tools you need is a 4 digit trig list, paper and a pencil (and an eraser!)  If you follow the standard arithmetic rules for signs and the trig functions you will never run into special cases. 




     

    From: Rommel John Miller <rommeljmiller@comcast.net>
    To: hannoix@att.net  Sent: Wednesday, May 29, 2013 6:27 PM
    Subject: [NavList] Re: Shooting Mercury

    Alan, you make a very valid and cogent point. A nice inexpensive solar powered that'll operate on just about any source of light is always a good thing to have around.
    But a slide rule can be fun if only due to its being arcane. They a fun to tinker with when you get bored, taking out a copy of "101 Problems for Celestial Navigation" and working them long hand and checking them on the rule.
    But consider this: NASA had great mechanical computers to call upon when Wernher von Braun designed, tested and flew the Apollo crafts, but in the end, and I am referring here to the ill-fated Apollo 13 mission, what did the engineers and the geeks at mission control rely on for those quickly need on the spot and reliable answers? The Pickett N600-ES check out http://airandspace.si.edu/collections/artifact.cfm?id=A19840160000, it appears that Jack Swigert, the engineer and pilot of Apollo 13's CM pulled his N600-ES out to verify the findings of mission control. Not from the movie, but an historical fact.
    and if a slide can save three men virtually stranded in space, it is good enough for me and my mundane earthly equations. Of course, I am an idiot for the versatile Math CAD program called Mathematica now in version 9.0 too, so I am not completely a Luddite, I just play one on TV. And speaking in nautical terms I am a relative Luddite. Now, can anyone tell me an inexpensive source for relative bearing grease?
    ----------------------------------------------------------------
    NavList message boards and member settings: www.fer3.com/NavList
    Members may optionally receive posts by email.
    To cancel email delivery, send a message to NoMail[at]fer3.com
    ----------------------------------------------------------------
    : http://fer3.com/arc/m2.aspx?i=124199


       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Get a NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.
    Email:

    Email Settings

    NavList ID Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site