|This is probably incredibly obvious to everyone but me, but:
I've had a 'Fashion Ruler' (C on the website linked above) since I started sewing -- when I walked into Britex and asked, "What should I own?" the woman who helped me said I could use it the straight, clear ruler for the time being, and that once I started altering patterns I would love having the curve.
I was tracing a pattern last night and it suddenly occurred to me -- use the curve! And lo and behold, although I have no idea how to actually use the curve properly, or what the various notations on it mean, if I slide the thing up and down, and maybe flip it over, any gosh-darn curve on my pattern will line up with some part of the thing!
My traced pattern came out looking exactly like the original.
I guess I have always thought, "Tracing, you know, like when I used to trace Snoopy out of the Sunday paper." But tracing is kinda like redrafting a pattern, only without changing it. I'd be pretty peeved if the lady at Kwik-Sew drafted my pattern by eyeballing it. I certainly shouldn't be eyeballing the pattern I'm actually using to construct my garment!
Newbies, I think the thing cost $15 so even if you never plan to alter your garments, think about buying one just for accuracy in tracing.