[coralpro]

The greenreader is a piece of junk but would have more benefit if it came with a bubble level that spand the top.
Your digital unit could be of some use but accuracy would depend on the area of the green it was placed at. Levels are dependent on their length of stance for accuracy and a small footprint is only going to take that footprint as a reference and with many greens having undulating or varying slopes it could be off considerably. Your idea of using it to train the eye for a particular green would work well. Don't knock plumb bobbing because it does work. It is just the applicant that causes it not to work. Before levels and lasers construction people used plumb bobbing to a great amount of expertise. Many a pro, as do I, still use this technique if they can't pick up the slope with the eye