Send the meter to a NIST-traceable calibration lab. The lab measures the meter against reference standards at multiple wavelengths and power levels and issues a certificate with the deviations. EXFO can help save both time and costs with an automated calibration test system that is designed for the verification of power meters, attenuators, sources and optical time-domain reflectometers (OTDRs). If we find a performance problem with the received instrument, we will let you know. You have to wait this warming up time, which is crucial for the meter.