Hello, thank you so much for your help, I really appreciated it. I tested the workaround that you suggested and at first, it seems to work. However, the K and Msv values obtained correspond exactly to the middle of the given range. I changed the range of these parameters several times but the result is always half of the given range for each one. Do you have any idea why this is happening? Fitting-K_and_Msv.mw