Test Your Math Skills! This Pop Quiz Clock is perfect for the math genius in you life! You don't really have to know how to solve the equations to know what time it is, but it sure is fun trying. This unique clock is a great conversation starter as well as an educational tool. ~ The Pop Quiz clock measures 11.5" in diameter. ~ It has a sturdy metal face. ~ It looks like chalk formulas on a blackboard. ~ Operates on 1 AA battery (not included).