Prism constant for Nikon?
Next silly question about the Nikon. It has options for Curvature and Refraction of OFF, 0.132, and 0.200 but I can't relate those numbers to any values I find in textbooks.
Does somebody have an explanation of what their units are, how they relate to the classical textbook numbers, or which one is better under what circumstances?
This is of no real help to your question, but you should be aware many data collectors will also apply the curvature and refraction correction so one should be sure that it is not applied by both the data collector and the instrument.
So I think this explains it. The refraction correction is typically 1/7th that of the curvature and opposite. Thus the following that I found adds context to the coefficients offered.
The coefficient of refraction is assumed to be 0.13 or 0.14 under standard conditions, but it fluctuates quite considerably.
The biggest influence on the value of the coefficient is the vertical temperature gradient
I assume there exists some situation that one would expect a lot of refraction in your sighting and thus the option for .20 but I don't know what that might be. We've always used the 0.14 coefficient for refraction.
From my days in uni, it's possible to determine the prism constant by doing a three peg test. You place three pegs in a line. You then measure the distance between them and over all using the same prism, the subtract the longer distance from the sum of the two shorter ones and that should give you the prism constant for whatever you were using.
