Being a little OC, I cleaned it just a bit with some fine steel wool. In a case like this, I put one of Mrs. Northwood's old magazines on the bench.
Tear off a dirty page, and you are good to go, over and over. I saw just a bit of dust/residue on a page, and the rule showed just a bit of improvement.
Put it in a box with some old Stanley marking gauges.
I rescued it from a steel box under a table at a junk show. Traded it for a Leonard refrigeration rat. They never appealed to me.