Oil prices are rocketing, and in desperate times we need to source our energy from renewable, "green" ideas. Solar powered calculators are available, but where's the dignity in that? I present to you: the hydroelectric calculator.
To fuel it, pour water in the bottle at the top. This water now has a head of several centimetres. In the central mechanism, a miniature Francis turbine (the most efficient turbine in the world!) takes advantage of the water flow, and generates a tiny current - giving the calculator enough life to perform even the most intense calculations. For about 30 seconds. Then you need to pour more water in.