Solar calculator can run as long as there is sunlight or other light source. Now, this type is much cooler, for it can run by using water. The major power supply component is in the front of it. The calculator can work after filling it with water and closing the cover.
The principle of power supply is based on the chemical reaction of electrolytes. It is safe and has no environment damage. Its function is just the same with the general calculator with nice price, only 8.99＄. But we don’t know how long it can run after filing water. That is the problem.