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Question 1 : Draw a pencil grid on any stone & lapping tell you if the stone is flat or not.

Question 2 : Looks like you are pushing the razor up & down the stone with your fingers on the heel &...

If you need to remove a lot of the surface, float glass & loose Silicon Carbide powder is the fastest way.
You can use wet n dri paper to replace the SiC but it never returns quite the same...