Three years ago, my family and I went to Russia on vacation. At that time, the USD-Ruble exchange rate was a really odd number, like 1 to 37.29. So instead of giving my brain math problems while on vacation, I decided to create a cheat sheet. And now, because the USD-Won rate is a very large number (and because the last thing I want to do is whip out a calculator on vacation), I've created another one. Basically, I created a Excel document, printed it on cardstock, folded it half, glued it together, and voila! A simple, fast and painless way to calculate how much you're about to spend in a foreign currency. Make one for yourself, make one for your friends. Dorky, yes. Convenient, double yes. Mine lives in my wallet for easy access.