A familiar example is addition of hours on the face of a clock, where 12 rather than 0 is chosen as the representative of the identity. If the hour hand is on 9 and is advanced 4 hours, it ends up on ⁠ 1 ⁠, as shown in the illustration. This is expressed by saying that 9 + 4 is congruent to 1 "modulo ⁠ 12 ⁠ " or, in symbols, 9 + 4 ≡ ≡ 1 ( mod 12 ) .