Hello. I can't understand some things in these two files attached with this thread. Firstly,in file "image 1",i don't know about the method of least sequares mentioned in equation 47. Secondly, in file "image 2",from where the equation 52 comes and how do we get the next equation 53. I want to discuss about these two pages if there's anyone already knows about this field or has special experience with it. thanks.