Before revision:  Next, the differences between estimated parameters are put into a 2 x 1 vector and is denoted by  V' = (ar - af, br - bf)  Next, covariance matrix S is estimated by summing Sr </big> and <big>Sf.
After revision:  Next, the differences between estimated parameters are put into a 2 x 1 vector and is denoted by  V' = (ar - af, br - bf)  Next, covariance matrix S is estimated by summing Sr