Compare your readings to the expected power range, typically around -3 dBm to -10 dBm for single-mode fibers; a sudden drop may indicate excessive loss or damage. Cross-checking with another OPM can confirm if the issue lies with the fiber or the meter. We describe NIST measurement services for the calibration of optical fiber power meters. Other general purpose light power measuring devices are usually called radiometers, photometers, laser power. While optical power meters are the primary power measurement instrument, optical loss test sets (OLTSs) and optical time domain reflectometers (OTDRs) also measure power in testing loss.