How To Determine IE of Your Sextant...

This will focus on and in support of land based observations through an artificial horizon where no long range horizon is visible to check alignment of your mirrors.

During the Winter I take a lot of sights from my backyard and it was only after discovering this approach I started to get the best accuracy. Unfortunately what the next iteration of determining my sextant's IE was the result of mucking around with the micrometer of my Freiberger that gave me huge unease in that I had misaligned the micrometer wheel by loosening a bolt head. Curses!!!

So with a blazing Sun, full shades on - Take readings of the reflected Sun both above and below the original - recorded the results, totaled the results and divided in half. The difference and when signed by the larger reading should be the IE of the instrument.

This I did once before and was getting very good accuracy on sights. The consternation that developed was that every time that I did it today and yesterday - I got different results! Both holding the sextant horizontally and vertically. I know that the sun is always moving from east to west, but why should the resulting IE change?

I will take additional readings throughout the day just to see how much it changes, maybe the changes are a result of altitude, refraction and diameter of the Sun - changing throughout the day.