http://www.eachbuyer.com/potato-fruit-clock-green-science-project-kit-kids-lab-home-school-experiment-p257984.html
So sorry I forgot put a link here...
Not a bad deal though. They are great for any learners, children, potato aficionados, or curious adults. My potato clock in my living room lasts several months typically, but as you know for your potato..... YMMV. With coupon NEWORDER5 get extra 5% off Look no further. Great product quality, that's solidly built. Best of all, its very affordable price. Buy today. Clock size: 65 x 31 x 11 mm Clock material: ABS Working principle: when different metals make chemical reaction, it leads to atoms movement between metals. This movement is called current. Note: Potato should be prepared by yourself. You can also try to use fruit juice, vegetable, coin etc to find unusual electric energy. 1 x Digital clock 1 x Connection cable 2 x Test glass 2 x Copper bar 2 x Zinc rod 1 x Scotch tape 1 x English user manual 1 x Original package