Bris sextant

[3] Sven Yrvind (Lundin) developed his Bris sextant as part of his quest for low-cost, low-technology equipment for ocean crossings.

It is made of two narrow, flat pieces of glass (microscope slides) permanently and rigidly mounted in a V-shape to a third flat piece of #12 welding glass to make viewing the sun eye safe.

The Bris sextant is calibrated at a known geographic position with a good clock and a nautical almanac.

As the day passes, one works the sight reductions backwards to develop exact angles for each of the images' tops and bottoms.

The Sun and Moon have approximately the same angular size from the surface of the Earth, and can use the same calibrations.