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Weems & Plath

3-Arm Protractor

3-Arm Protractor

Regular price $54.95 USD
Regular price Sale price $54.95 USD
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The piloting technique with the highest accuracy is a "3-body fix" using a sextant to measure the two angles subtended by the three bodies. This tool offers the fastest way to plot that fix.

Procedure:
With three charted bodies (A, B, C) in sight that can be identified on the chart, use the sextant horizontally to measure the angles between A and B and then B and C.

The center arm of the device is the reference. Set the left arm at angle AB and the right arm at angle BC, and then holding the set angles in place, align the three arms to cross the three bodies sighted. The center of the protractor then marks your position.

For a brief explanation of three body piloting see article

To see the high precision instrument that forms the basis for this device click US Navy Station Pointer, which is an instrument of ours on display at the Institute of Navigation's Virtual Museum.

See also Notes on plotting tools.

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