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
    or...
       
    Reply
    Puzzled by Douglas Protractor Instructions
    From: Martin Gardner
    Date: 2016 Apr 25, 11:34 -0700

    I've got a WW II vintage Douglas Protractor.

    There are instructions on the cardboard sleeve which start off: To lay off a course or bearing - Use the left side as a ruling edge and the graduation in italic figures on the meridian or parallel - rule the desired course or bearing. For example try 10°, 170°, 230°, 350°. The left edge can always be distinguished by the writing "Douglas Combined Plotter and Parallel Rule"

    This sounds fine, and it's easy to lay off a course on the meridian.  But the instructions say "on the meridian or parallel" - why "parallel"? Thousands of these things must have been deployed, so it's not a typo.  How did they intend using a parallel? (Of course you could add or subtract 90° to use a parallel, but was that what they meant?)

    (Here's a webpage with images of the protractor and the cardboard sleeve http://www.historicflyingclothing.com/en-GB/ww2-raf-personal-equipment/air-ministry-douglas-protractor/prod_14854)

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    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:

    Email Settings

    Posting 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