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I’d be very careful about going near the dial with abrasive paper of any description. I assume the part your referring too is the plastic window on the front and not the actual dial underneath.
if your going to try removing scratches practice on something like a piece of Perspex first.
very fine wet 2500 grit very lightly circular motion to start with which will blend out fine scratches but completely dull off the face then use a polishing compound to buff it up then use some standard polish. If your referring to the actual dial under this cover then I’d say leave it well alone.
if your not removing scratches then simply clean it up with a damp or standard polish. You can take it apart and do the inside too. I can’t emphasise enough to practice on something else first before attempting to buff out scratches
Another easy way, one which is used by watchmakers to clean clock dials, is to use plain Brasso, or toothpaste, just rub it on the scratched surface using a soft cloth and it will come up gleaming bright and scratch free, after a bit of work,no risk of deeper scratching by using abrasive paper, to finish off if needed, ( it wont be, but this also works) is to splash a few drops of brasso onto a piece of cardboard and go over the dial again. The cardboard seems to give it an even brighter clean finish.
We used to "card " our brasses on our belt buckles this way when I was in the Army about two hundred years ago.