Finally I can add something of help. I think. There were some spots etched into the under side of my windscreen above the master cylinder deep enough to feel with my fingernail. I got rid of them as follows. You will need three different compounds. 3M "Perfect It", Meguairs "Diamond Cut 2.0" and Meguairs "Swirl Remover". Each has decreasingly finer cutting ability. Use some pads cut out of a Tee shirt. Terry cloth is too coarse. Remove and wash the screen with soap and water. Dry. Start with the Perfect It using medium pressure. Do not rub just the ding but rather carry the rubbing out beyond it. This prevents creating a depression which will cause an aberration in the screen. Rub it til it's gone. Wash and dry again. Now rub with the Diamond Cut. I did the whole underside with this so it would be even. Wipe clean with more tee shirt. Then go over the entire surface with the Swirl Remover until it's no longer wet. Wipe off the haze and you'll have an absolutely clear ding free screen which looks brand new. A word of caution. Unless you're very, very good with a buffer do it by hand or you'll run the risk of "burning" the screen and that's a real mess. If you have deep scratches wet sand with 2500 wet using a flexible rubber pad to spread the pressure before doing the above. And if you F--- it up a new one goes for $150.00. At least you tried.