Howdy ,

Here's pic of the type of calipers i use to graduate plates ... set at 6 mm , run them all over the plate and check the gap with a scale / ruler ...a larger set is needed if the ribs are still in place on the top or back ....take notes and then use yer cabinet scraper to bring the graduation into yer desired specs ...easy enough to do and the results can be very good ...be sure to burnish yer work with a thick piece of belt leather  ...