NavList:

By the way, back when I was messing around with this a decade ago, I recall reading an article from c.1905. The article proposed something like your concept of a set of prisms that a navigator could purchase and have available to re-calibrate a sextant on the "far side of the world". That's all I can remember about it right now. We may well have discussed it in NavList messages ten or twelve years ago. Just so there's no misunderstanding, I think the principle is sound. My only issue was that I couldn't make a practical implementation.

Frank Reed