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    Re: Pointless? Optimisation - Intercept Plotting
    From: Paul Hirose
    Date: 2019 Feb 3, 11:27 -0800

    On 2019-02-02 5:01, Michael Bradley wrote:
    > The Douglas type Protractor has been tried, but by its nature it has bearing 
    markings on its edge which confuse matters, and in needs a copious supply of 
    meridians which you don't get on a plotting sheet.
    I have not found the single meridian of a plotting sheet a problem with
    the Douglas (square) protractor. Say the azimuth of the body is 231°. If
    the protractor is oriented to north, the top and bottom edges of the
    protractor are oriented for a line of position at azimuth 0 or 180°. To
    change that to the required 231°, rotate clockwise, counting by tens and
    ignoring the numbers on the protractor: 190, 200, 210, 220, 230. Go one
    more degree to obtain 231°. Now with the help of a straightedge the
    protractor can be moved to the assumed position without changing its
    orientation. Place one of the correctly oriented edges on the AP, then
    use the millimeter scale on the straightedge to slide the protractor
    toward or away as required. This lets you plot the LOP without first
    drawing an azimuth line to the body.
    The 5 inch square protractor works well with 8.5 by 11 inch plotting
    sheets when there's not much space.
    Another shortcut is to use azimuth angle Z directly. For example, in the
    northern hemisphere a traditional sight reduction would give Z = 129 in
    the previous example. When the protractor is oriented north, the left
    and right edges are oriented for a LOP at Z = 90. But you need 129, and
    since the body is west of the meridian, the protractor must be rotated
    counterclockwise.  Count by tens: 100, 110, 120, 130. Then turn back one
    degree to get 129. This simple trick eliminates the azimuth rules, and
    it works with any protractor.

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