These self-checking Math Machines make math so simple, kids can teach themselves! Children just press the equation buttons…and the answers pop up for immediate reinforcement! You get 81 equation buttons in each unit, locked securely into the tough 8 1/2" x 9 1/2" plastic frame. https://www.lakeshorelearning.com/products/math/basic-operations/addition-machine/p/LC1166/?srsltid=AfmBOoqrWAHzn4vvk8V762MbvJZnaBvr6Pn5U7vQkcZ3mdB-oPgFySHW