This is the raw per-collection-interval delta for CRC errors on received frames: it holds how much the underlying counter (counts Fibre Channel frames this port received whose cyclic-redundancy-check failed, meaning the bits were corrupted somewhere between the sender and this receiver) increased during the single most recent sampling interval, rather than the all-time total. For one specific FC port's current error-statistics object, watching this delta rather than the lifetime counter is what lets monitoring catch a fresh burst of errors quickly instead of waiting for a slow-moving cumulative total to visibly move. For example, a delta of 6 in one interval on an otherwise-quiet port is a much stronger signal of an emerging problem than the same 6 buried inside a lifetime count of 50,000.