It's tiny, it's light, it's solar powered, and it has about the same functionality as a TI-30. In other words, it's a very basic scientific calculator: no complex numbers, linear algebra, calculus, solvers, or exact math (except for rudimentary fractions). Note that it has an old school interface. If you want to do the sine of 45, you don't type "sin(45)", you type "45 sin". But it does use algebraic notation for basic arithmetic: "1+2*3=" will return 7. Basically, it operates like a pre-2000 scientific calculator.
How tiny is it? It's about the size of a man's wallet, but half as thin. It's even thinner without the protective cover. I don't notice it when it's in my pocket. I wish it were all black instead of having a white shell, but at least it isn't pink or some other painful color.