Is there a math-lover in your life looking to up their nerd décor? This math wall clock by Decodyne puts a spin on traditional analog wall clocks and is one of our favorite math teacher gifts. Each hour is represented by an equation. It’s simple black design and chalkboard style equations blend in seamlessly with any décor: home, office, lab, or classroom. d=2r where d is 11.5 inches (diameter of the clock is 11.5 inches). The clock has no wires or cords and runs on an AA battery. No nerd gift will top this for the math junkie in your life.