How to fit a curve when i have only a drawing and the corresponding values?

[DrilonShabani]

As it can be seen in the attached picture, I need to find an equation to fit this curve if I have only the data from the picture. Since this is a graphical method, I can't have a high accuracy but I need a generalized function that would give me the value for every point. As you can see, the values in Y-axis are not linear so I have no idea about the type of the function.

[ValeryOchkov]

Create at first vectors X and Y using for example Paint

[ValeryOchkov]

Or as first step (sorry - I have no time to show last steps - later!)

[ValeryOchkov]

[ValeryOchkov · Accepted solution]

It not need a lot time

[DrilonShabani]

Perfect. Thank you very much

[Fred_Kohlhepp]

If all you want is to create a function to use for other calculations then the methods Valery outlined are sufficient.

There is a program, "CurveExpert" that will take your tabulated X,Y data and present a list of functions and how well they fit (along with the least square coefficients that best fit your data.)  This can be quite helpful if you need a function definition for some reason.

[DrilonShabani]

I just downloaded it .. it is reaaaalllyy nice.. thanks a lot