Building Logistics Function from Data set

Are there any more elegant ways to build a logistics function to model data.

Here is my current solution, however you need to assume the assymtote (m value)

http://i1112.photobucket.com/albums/...icki/Scan1.jpg

http://i1112.photobucket.com/albums/...icki/Scan2.jpg

Is there are a similiar way to build a linear first order model from data?

Thank you