I don't think you need to go too strong on documenting the 0.01 here.  The tol value already sets an accuracy limit for the resulting Interpolant.  The 0.01 factor means that any additional numerical inaccuracies in building the lookup table are _much_ smaller.  So I think I'd recommend just putting a comment to this effect in src/Interpolant.cpp where we define these values and leave it at that.

That said, we probably ought to have some kind of documentation for the Interpolants in general, so if you'd like to do that on this branch, that would be great.