One of my neighbours gave my daughter a Mitsubishi Colt that they no longer needed.  It had a few faults that needed fixing before it could be taken for it’s annual test.  On of the faults was a nasty wide scratch on the windscreen.  Presumably a faulty wiper blade caused the scratch which was approximately 5mm wide covering the full curve of the drivers side windscreen wiper.  It wasn't deep, but was  very obvious and was directly in-front of the drivers vision.  Unfortunately I forgot to take a photo of the scratch.

  I used the motor out of an old cordless drill and made a pad cut out of some old jeans mounted onto a plastic arbor.

As a cutting compound, I used Farecla G3, which was chosen simply because it was the only cutting compound I had.

I left the motor and wipers running for about 3 hours.  I periodically checked the scratch  and adding fresh compound when necessary.

This photo was taken after the polishing.  The scratch has been completely polished out.