"doubt about K_sigma transform"

Hi，I check your code for k_sigma transform. And I find in sigma process，cvt_b compute by difference of offset and divide by k_a. I think may be we need not divide by k_a. Is there any consideration about this. Thanks.

cvt_b = (sigma / (k ** 2) - sigma_a / (k_a ** 2)) * k_a

Start by tracing the k_sigma transform and sigma process to the point where cvt_b is computed. Verify the stated formula and determine whether the division by k_a is intentional; done means resolving the mathematical question and documenting or correcting the behavior.

Written by the indexing model from the issue text.