To respond to the original post, if you need to be somewhat accurate, I'd trace it CAD, then make sure the dimensions are correct in the CAD file. I use Adobe's measure tool often for quick and rough numbers.
Adobe Pro is an expensive program, but I've found in the past couple of years that it is well worth the money, for the measure and scale tools as well as other little pieces of goodness. I particularly like the stamp tool, which I've created a stamp for my seal (from a cad file) and am able to put it on any pdf with a few clicks, print and sign.
I too have used a planimeter, I'm 32. I've also used a slide rule, however that one was just out of curiosity. The functionality of both tools are amazing to me.