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    Re: Horizontal Angle and the Hand Bearing Compass
    From: Michael Dorl
    Date: 2011 Jun 04, 06:56 -0500

    On 6/3/2011 3:54 PM, Greg Rudzinski wrote:
    > Try taking a horizontal angle using a hand bearing compass the next
    > time out sailing. This only requires taking the difference between two
    > bearings and plotting the arc of position. This adds a third line of
    > position to the pair of magnetic bearings and will act as a deviation
    > check. My favorite way to plot a horizontal angle is to take half the
    > distance between mark A and mark B then divide by the SIN of the angle
    > between mark A and mark B. The result is the radius of the circle
    > which passes through the observer and marks A & B. Plot the circle by
    > first marking off the circle center using the radius distance arced
    > off marks A & B. From the circle center then trace the cirlce that
    > will pass through mark A & B and the observer. I find this technique
    > very quick using only a divider compass and pocket trig calculator.
    > Greg Rudzinski
    Is it really as simple as this?   I realize that since you know he
    bearings of the lines from your position to marks A & B, the angle
    between A & B and the bearing of A-B, you essentially know the three
    angles in the triangle (position - A - B). Therefore the problem is
    solvable but off hand it would seem that the other angles would enter
    into the solution.    Surely there are other positions from which the
    angle between A & B are the same but with different bearings.

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