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Or pick up a cheap 100x microscope (toystores have em ~$10-15) and learn to identify each hone's scratch pattern. That plus the water wave Glen mentioned is how I tell if I'm affecting the toe and...

You sure the rust wasn't simply deeper in some areas than others?

If it was your sanding would have produced a wavy blade that could easily be trued with some time on a belt sander or low grit...