Re: what is a best fit line?why is it useful?

A best fit line is used to connect a set of coordinates on a graph in a way 
that allows us to see a relationship clearly. It is basically a "best 
estimate" of what a line would look like if all the data points fell on it. 
Why don't data points always fit? Because measurement is never a perfect 
thing. There is always a margin of error in whatever we measure. If you 
cook, for instance, and the recipe requires one cup of milk, I bet it's 
seldom that you use precisely that amount - you fill the cup up to about the 
one cup line and go for it. Data are like that too. In measuring the speed 
of an object, the position of a particle, the length of an organism, there's 
always a little uncertainty. Best fit allows us to take these uncertainties 
into account, and give us a start on refining the data for more accuracy.

To see a very simple and practical example of best fit and how it works, go 
to http://
www.saburchill.com/physics/chapters/0073.html

Thanks for a great question.