Probability (quality) of a Fit function

From: Steffen Wenzel (wenzel.steffen_at_gmx.de)
Date: 06/30/04 

Date: Wed, 30 Jun 2004 12:13:43 +0000 (UTC)

I have a dataset of two reliable values, punctuality (y(x)) and
movements of aircraft (x). Therefor I built a Fit function with
Mathematica. Now I want to know how good is the probability of the
term y(x) of the Fit function for any terms of x.

How I have to proceed next... any helps !?