Often the autoscale on the charts is not very useful. For example if I have a workout with a sprint (or an erroneous high point) the scale makes it very hard to read because the rest of the workout is then compressed vertically. It would be nice to be able to adjust the vertical scale/zoom so that it is scaled appropriately of what is on the screen. You could zoom manually (the way the horizontal zoom works) or just edit the axes values.
Another related feature would be the ability to drop a "horizontal" line at a certain value (e.g. LT, or goal pace, etc.) which would also solve the problem of Y axis readability.
This problem is exaggerated if you view graphs on a phone because the graph is already compressed due to the smaller screen size. I posted this in the WebApp group initially but I think it applies everywhere so I'm re-posting here.