Guide to gauge

I keep running across the same questions again and again about gauge, swatches, how to make a certain yarn work with a pattern etc etc.

I thought i would compile a short(ish) guide to gauge and post it on my blog as an easy reference. I know there are a lot out there already i just thought i would add to it.
here is mine:
and here is a lovely article from knitty:

please if you have any tips, additions or corrections let me know or add to this thread.

Thank you for doing that. I’ve bookmarked it!