Turn the vital calculations (R) into functions which are dependable on the changing parameters rather than using static, local assignments for them. Use those local assignments only for values which can be calculate using the changing parameters. That is , write R(L,B,hf,....):=... or whatever the parameters necessary to calculate R are.
Maybe it would help to split the calculation using some subfunction as the implementation for the calculation of R is rather lenghthy and hard to read.
