The onscreen visual resolution has nothing to do with the under-the-hood resolution of volume. That invisible resolution is incredibly high. The visible resolution cannot possibly keep up to this. But luckily this visual resolution has nothing to do with what you actually hear. I counted about 220 steps in the volume slider (now that it's no longer visible with "MIDI" values, just dB). If you're using TrackAutomation HyperDraw (and adjusting nodes with the mouse), then the track height makes a difference regarding what resolution you can move the mouse. If you hold down Control (you have to press this key AFTER you hold down the mouse button, otherwise you'll get the contextual menu), then you can slide nodes up/down in those finer increments no matter what the track height is.