One common problem is zero point failure, which refers to the case in which no optical signal can be measured, but a meter reading significantly different from zero occurs. This could be because of contamination on the detector, or incorrect calibration. 2) Set the meter wavelength to match the signal. 3). In this video, we explain how to repair an Optical Power Meter that powers ON but does NOT show any optical power reading. Knowing a few problems and how to address them can help ensure your results are reliable. PM100USB 1 General Information The PM100USB Optical Power and Energy Meter measures the optical power of laser light or other monochromatic or near monochromatic light, detected by an appropriate sensor and is compatible with all Thorlabs “C-Series” Photodiodes, Thermal Sensors, Pyroelectrics.