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
    Angles without a protractor
    From: Sean C
    Date: 2012 Oct 12, 04:29 -0700

    Apologies if this has been mentioned before, but I just learned a method for drawing/measuring angles using only a ruler. Thought some here might be interested.

    It turns out that if you have an angle you want to measure, you can mark each of its rays at 3 inches, measure the distance between the two points, multiply the result (in decimal inches) by 20 et voila!

    I used the following method to draw an angle of 35°: I drew a roughly horizontal line on a piece of paper and marked it 3" from one end. I then constructed an arc by measuring and marking a few points, all at 3" from the same end. Next, I measured a secant line with a length of 1.75" (35/20) within the arc with one end at the first 3" mark I made on the horizontal line. I marked the other end and connected the vertex with this point.

    Upon measuring the angle with a protractor I found it to be 34°. Not perfect, but would probably do in an emergency. And if I had spent more than a couple seconds marking it out, I may have achieved better accuracy, IDK. Of course there are other methods to achieve the same result. Anyway, someone who knows much more about math than I do figured out that the maximum error should be about 6% for a 90° angle. Again, IDK if that's correct.

    As far as I can tell, the method will work for any unit of measurement. Hope someone finds this mildly interesting, if not useful. :)

    Cheers,
    Sean C
    ----------------------------------------------------------------
    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
    ----------------------------------------------------------------

       
    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