Originally Posted By: Mark_R
Originally Posted By: rafowell
Originally Posted By: Russ
Gravity doesn't work well enough in a small boat bouncing around at sea. I was a tad confused by the picture of the improvised sextant.
Measuring the angle between sun/star/planet and the horizon is much more consistent than using gravity. A sextant allows for ship movement while allowing an accurate elevation angle.

I don't think any measure of gravity (local vertical) was required.

The way that type of signal mirror sight works[1] is that you align the reflected light beam from the sun with the line between the hole in the mirror and the hole in the sight.

My guess is that he did that, with the horizon as the target, then recorded the mirror tilt angle, and doubled it to get the sun to horizon angle.


... There would have to be some extra mathematics to compensate for the vertical travel of the center of the mirror's sighting hole, but not impossible with a working knowledge of trigonometry (and mathematics tables).

Good point - I had visions of trying to pivot the mirror about the lip of the tin, to keep the sighting hole near the pivot axis, but as you point out, the consequences of pivoting about an axis offset from the center hole are elementary trigonometry - annoying but fully calculable. While trig tables would help, they aren't essential - they can be reconstructed by, for example, Taylor series expansion.
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A signal mirror should backup a radio distress signal, like a 406 MHz PLB (ACR PLB) (Ocean Signal PLB)