Hi, I'm Kevin Hall and I'm bad at math. (Boy, does it feel great to finally get that off my chest.) That's why this nifty little solar-powered Credit Card Calculator actually has quite a bit of appeal for me — I could carry it around in my wallet and work out a tip or a grocery bill as I go. It's also a decidedly nice design, looking enough like a credit card that maybe it'd appeal to the spy in all of us, as well.

The best part? It's an easy-to-swallow $6 right now.

Credit Card Calculator, via Better Living Through Design