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It is a stereomicroscope--a Zeiss Stemi SV8. Its advantage as a stereomicroscope is that I can quickly focus by moving the blade up and down to focus and can rotate the blade to change the light...

I've shown this a few times already, but it really is relevant to what was described here. Below is a poorly made (by me) video of a factory edge that also had some issues. You can skip to 1:40 to...

Here is the answer to the question of why he looked at the edge.

Curiosity...

It causes and solves a lot of problems.