Poke Test Video?

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Is there a good video demonstration of the poke test out there somewhere? I have seen it described in numerous places, but still don't know how to interpret my results. 

If I poke in about half an in, it comes 'mostly' back. So is the dough underproofed?

Thanks for the link. Very helpful.

But yeah, I am not sure what that guy was thinking. He keeps poking the dough so that you can't see his finger.