You need to calibrate your Optical Power Meter at regular interval to ensure the reading is correct. Pre-Calibration Inspect for, and if found visible damage or debris that may effect the accuracy of the meter remove. Knowing a few problems and how to address them can help ensure your results are reliable. These measurements are accomplished using either collimated-beam or connectorized-fiber. OPM interface: insert the fiber to be tested, test the optical 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. Below are general answers on how to operate, maintain, and calibrate an optical fiber ranger from the list of GAO Tek's optical power meters.