Make sure you have a new 3-volt, lithium battery, number CR2032, to insert. Open the battery door on the back of the meter, remove the old battery for at least 20 seconds, and press any button on the meter. Insert the new battery with the “+” sign facing out. Snap the battery door back into place. Press the on/off button, and the meter will beep. Setup and hour are flashing on the display. If the date and time are correct, press and hold the on/off button for about 4 seconds. Release the button, and you’re done.