The scroll wheels on computer mice seem to be highly variable in terms of the precision with which they locate the cursor. I know this because today’s invention is a technique for quantifying these errors.
Open up your favourite browser and point it at Google maps. Now you can centre the map on some prominent feature (I use a huge, white-roofed exhibition hall in Vancouver). Next, secure the mouse to the desk (duct tape works, as ever) and use the scroll wheel to zoom out to ‘space’ and back a fixed number of times (say 5). Record the new screen centre location on the map (this will have changed, in general, due to sloppiness in the way the scroll wheel mechanism works). If you can stop the hypnotic process of zooming in on terra firma, eventually you will have characterised the on-screen precision of your scroll wheel.
This probably isn’t important for most users, but I understand that it affects some games players’ performance. In addition, if you have identified a brand of scroll wheel which operates with known, high accuracy, this could then be used to detect any hand tremor in users of an untethered mouse.