This is the lowest value recorded during the current performance-monitoring interval of the differential group delay (DGD) measured on this channel during the current performance-monitoring interval, expressed in picoseconds, reflecting how much polarization-mode dispersion is spreading the two polarization components of the signal apart in time. The lowest DGD seen in the interval shows how good conditions get on this fiber, useful context for distinguishing a fiber with consistently low PMD from one that merely has occasional calm moments. For example, on a newly installed, low-PMD fiber, an admin would expect differentialGroupDelayMin to stay very close to zero across most intervals.