I'm actually not convinced this line (or the similar one below that does this delta2 calculation in another place) is right.  My assumption had been that if someone says units are something like radians, then what they mean is that k is in 1/radians and Delta^2 is in radians^2, so that when you multiply by k^2 you get something unitless.  In that case, the factor in front should be ```k**2```, not ```(self.scale*k)**2```.  Have I gotten something confused here?