Welcome to the NavList Message Boards.


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

Compose Your Message

Add Images & Files
    Re: The "golden rule of three" - what's that?
    From: Don Seltzer
    Date: 2018 Feb 11, 23:35 +0000

    'Teacheth, by three numbers given, to find out a fourth, 
    in such proportion to the third as the second is to the first. 

           RULE. - First state the question; that is place the 
           numbers in such order that the first and third be of one 
           kind, and the second the same as the number required;... 
           Multiply the second and third numbers together, and 
           divide product by the first, the quotient will be the 
           answer to the question...' 

    In simple terms, how to solve a ratio problem.

    Today we would most likely express it as a very simple algebraic 
    equation. In earlier times it was taught as part of basic arithmetic 
    as a rote procedure; put the known values in a specific order, 
    mulitply, divide, and you have the answer. 

    Don Seltzer

    On Sun, Feb 11, 2018 at 6:19 PM Tony Oz <NoReply_TonyOz@fer3.com> wrote:


    I'm reading the "History of Nautical Astronomy", Mr Cotter describes the state of (apparently insufficient) mathematical literacy of seamen of 15th century like that:

    ...importance in introducing to the English seamen ... the elements of mathematics beyond the golden rule of three.

    What is that?

    Recently I had some hard time guessing what the "butterfly multiplication method" is. We, in Russia, were never tought anything like that.

    Please comment.



    View and reply to this message

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

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

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

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

    Email Settings

    Posting Code:

    Custom Index

    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