Got mine through Masterpiece Models. Being only one state away, they got them here in record time. Surprised the heck out of me. Up to this point I'd been using my architect rule, which works for some scales, but not others very well. For the others, it's break out the calculator and play with the numbers.
I still recall my Mechanical Drawing teacher; "Your scale is not a straight edge! If I catch you using it as such, you will be counting on stubby fingers!" Ah, the good old days, when threats were part of the curriculum.
"Why do I do this? Because the money's good, the scenery changes and they let me use explosives, okay?"