It is easier to comprehend when shown in a picture:
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And that's it! The spirit-level just stuck itself to the hotshoe at some point and is of no special use here. You can use a variety of lightsources, the closer to daylight, the better. Flash works just fine. No need for contraptions like tripod or copy-stand. I'm using this in my living-room on the coffee-table and can put everything away in a few seconds. As I don't have a dedicated man-cave for such tasks, this is a big plus.