I put in enough significant digits to get me close to the distance I wanted. I also didn't want to compound rounding errors, though I imagine Excel keeps all of the decimal places. On my chart there is one more column with the degrees of turn so I can mark the focus scale on the Mercury and I wanted that as accurate as possible.
Regarding the 'true' focal length, yes I am aware that is dependent on the lens. Since I can't know the exact focal length of others' lenses, I used the default value from Schneider. If one wants to be exact they can measure their lens and edit the values accordingly. Or instead, I guess I can just not publish the rough values at all here? Sheesh.
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