Press On/Off button for 3 seconds to turn on. Hold the unit so that the sensor is directly exposed to sunlight. Press the Measure/Adjust Button for 2 seconds until you see the sun icon flashing. Release the button and wait 3 seconds. When the sun icon disappears, the unit displays the UV Index. The unit will automatically display a count down until an alarm will sound to remind the user to take action to decrease risk of sunburn and will display the % of maximum suggested sun exposure to avoid sunburn.