This is the instantaneous, most-recently-sampled value of the accumulated chromatic dispersion measured on this channel during the current performance-monitoring interval, expressed in picoseconds per nanometer (or per picometer for the averaged/min/max readings), reflecting how much the fiber has spread the signal's spectral components apart in time. A live chromatic-dispersion reading lets an admin see the present dispersion compensation the coherent receiver's DSP is having to apply to keep the signal readable right now. For example, right after commissioning a new long-haul span, an admin would check chromaticDispersionInstant against the fiber vendor's specified dispersion coefficient to confirm the measurement matches expectations for that fiber length.