Bits and Pieces - Decorative Hanging Math Wall Clock - Mathematical Formulas Funny Clock Each number space features a mathematical equation to keep your math skills sharp. Black clock face is made to look like a chalkboard with each math equation painted to look like white chalk. The perfect gift for your favorite brainiac. Made of plastic, with silver-toned metal hands, requires 1 AA battery, not included. Measures 11-3/4" in diameter.