Prime Time Numbers Calculus Math Unisex Analog Watch Prime Time Numbers Calculus Math Unisex Analog Watch The Prime Time Watch only uses prime numbers to express the time. Naturally, 2, 3, 5, 7, and 11 remain untouched, but for the numbers 4, 6, 8, 9, 10, and 12, the watch really gets imaginative. Features a 33mm diameter face, genuine leather band, and Japanese quartz movement. Battery included, and comes boxed in a beautiful tin display case. Protected by a 2 year Asurion warranty (see details below) Click on "The Unemployed Philosophers Guild" near the product title to see more great gifts. UPG truly has presents of mind.