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: Cylindrical Slide Rule tube poll
    From: Gary LaPook
    Date: 2010 Jan 25, 21:32 -0800
    An easier way to check the computation on a Bygrave is to do the same computationn on a calculator since this allows you to check the intemediate steps.

    Just use the standard Bygrave formulas in the three step process following along on the form I have posted and using my terminology.

    First calculate co- latitude and save in a memory on the calculator. If you are using a value for hour angle that is not a whole number of degrees you might want to make the conversion to decimal degrees and save it since it will we used twice. If you are using whole degrees then this step is not useful.

    Then you calculate "W" using the formula:

    tan W = tan D / cos H

    and sum it to the memory where you have saved co-latitude which is then X and then make any adjustment necessary to convert X to Y. (If you are just making trials you can avoid this step by your choice of the trial values.) There is no reason to store W itself since it is not used again. You can then convert W to degree and minute format to compare with the Bygrave derived value.


    Then you compute azimuth angle using the formula:

    tan Az = (cos W / cos Y ) x tan H.

    If you want you can also convert Az to degree and minute format to compare with the Bygrave.

    The last step is to calculate altitude with the formula:

    tan Hc = cos Az x tan Y.

    Then convert to degree and minute format to compare.






    (When entering values in the format of degrees minutes seconds, change decimal minutes to seconds, 6 seconds per tenth of a minute, in your head  before punching in the assumed latitude, declination  and hour angle if necessary.)

    Using whole degrees for declination, assumed latitude and hour angle, using a TI-30 with only 3 memory locations the key strokes are:

    90
    -
    Assumed Lat
    =
    STO 1  (co-latitude stored in memory 1)

    ---------------------------------------

    Declination
    tan
    /
    H
    cos
    =   
    inv
    tan    (computed W)
    SUM 1 (X or Y now stored in memory 1)(change X to Y if necessary)
    cos
    /
    RCL 1  (recalls Y from memory 1)
    cos
    x
    H
    tan
    =
    inv
    tan (computed Azimuth angle)
    cos
    x
    RCL 1 (recalls Y from memory 1)
    tan
    =
    inv
    tan  (computed altitude)


    2nd
    D.D - DMS (changed Hc in decimal degrees to degrees, minues and seconds)



    done

    gl
    Hein Bodahl wrote:
    On 24.01.2010 23:32, Hanno Ix wrote:
      
    Hein:
    
    These are nice scales. However, is there a way to check the accuracy?
    It appears to me  computer generated scales depend on the accuracy and resolution of the particular printer one uses, no?
        
    
    Hopefully, an probably, any inaccuracy in the printer would be
    consistent enough over a few sheets. The resolution would of course have
    to be good enough to reproduce the scales with sufficient detail.
    
    I just realized that the separate scales I attached have different
    orientation. They should of course both be printed the same way as a
    printer most certainly deviates in accuracy in different orientations.
    
    As for testing I guess the easiest way is to test them against a
    calculator like this:
    http://www.coastalsailing.net/Resources/Navigation/Calculators/SunInformation.html
    
    I guess the greatest inaccuracy would occur in cos of a small angel and
    cot of an angle of about 45.
    
    Hein
    
    
    
    
      

       
    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