Whenever you find yourself doing metal fabrication you'll come to a time when you need to make a razor straight cut. Unfortunately most of us don't have a big 'ol "stomp shear", so we need to use a power or hand tool. It seems no matter how many times I measured, set my tools up, got comfortable, did practice runs, etc. I could never get a perfectly straight line when cutting longer cuts on sheet metal. Recently it clicked in my head to utilize an old trick when making straight cuts with a plasma cutter.