Home / Calculus / Introductory Ideas / Average Rate of Change; Better Estimate for df/dx at x=a B. Average Rate of Change; Better Estimate for df/dx at x=a Average rate of change and better estimates for the derivative. Topics in this Section B.1 Average Velocity for a Trip B.2 Average Velocity Over Any Interval B.3 Generalizing Average Rate of Change B.4 Lab 1 Introduction: Approximate & Bound Error for df/dx B.5 Lab 1 Activity: Approximate & Bound Error of df/dx