If you tend to do your math in the basement or someplace where no sunlight could possibly shine into you might need an alternate form of energy. Now no one likes those pesky battery powered calculators, so here is a water powered one.
I have had those times with the really cheap solar powered ones where I have to tilt it in just the right way to get it working again. However, generally most of the time it gets the job done. I'm not sure I see the need for a water powered device such as this.
Just put water into the rear power pack and then insert the stopper panel. The electrolytes in the water will generate the power necessary to keep the calculator going. It is perfectly safe and features a large LCD screen.
Water-Powered Calculator Sounds Dangerous [via gearfuse]