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David,

When making an observation without an optic it is easy to be off on line of sight (collimation)  when using just a ghost ring. A sight tube is a much better way to keep things centered. Remember to apply index error to the artificial horizon sextant reading then divide by 2 before applying the refraction correction. Of course there is no dip correction for height of eye. The beauty of the artificial horizon observation is that there is no uncertainty due to height of eye, anomolous horizon refraction, or perpendicularity. Systematic errors are also cut in half when the observation is divided by 2. So expect LOPs to be closer to the actual position vs. using a natural horizon.

Greg Rudzinski