Received two of these today. When tested against a known level, they deflected a half bubble and a full bubble respectively, and the flat surfaces on the back were slightly convex, preventing them from laying flat on the surface being tested and wobbling. The only reason I'm giving them two stars instead of one is because I was able to restore the back with a flat file and flat lapping block to make them look like they should have come out of the box. If you're not willing to do something, they're practically useless.
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