Here are three graphs for examples, these are AE 7.0 so it'll be a bit different. I believe these graphs are how your Value: Scale should be (it's a different system in 7) The first is a linear zoom, the second has Ease Out on keyframe 1 and Ease In on keyframe 2, and the third is the altered graph with the exponential curve. Hope this helps!
Even Zoom
Eased Graph
Exponential Graph - Not shown, but the first keyframe bezier handle is at (0%,0f) and the 2nd keyframe handle is on (0%, 25f)