In the Clock mode Press "Left button" for 3 seconds it will enter the 12/24 hr time mode setting, go on to press the left button again to exchange 12/24hr. After the confirmation please press the right button to enter the hours setting When the hours number is jumpiness, press the left button to set, but if press the right button again it is to set the minutes number, when the number jumpiness, press the left button to set. After the clock setting finished it enter into Odometer mode.