Here are some best practices to extend the life and performance of your optical power meter. Keep your meter in a cool, dry environment, free from direct sunlight and heat. If an empty battery indicator mean the power is almost out please replace it with a new one. Other general purpose light power measuring devices are usually called radiometers, photometers, laser power. REF/dB key: Short press the dB to switch unit, click once nW/dBm/dB to enter the upper clear data, press and hold until REF is displayed on the screen, and set the current optical power as reference value, enter the relative optical power test mode, the screen will display the setted reference. A series of beeps will indicate that the. oration, are to be maintained in strict confidence.