An average counter that shows how many items are processed, on average, during an operation. Counters of this type display a ratio of the items processed to the number of operations completed. The ratio is calculated by comparing the number of items processed during the last interval to the number of operations completed during the last interval.
Formula: (N -N )/(B -B ), where N and N are performance counter readings, and the B and B are their corresponding AverageBase values. Thus, the numerator represents the numbers of items processed during the sample interval, and the denominator represents the number of operations completed during the sample interval.
Counters of this type include PhysicalDisk\ Avg. Disk Bytes/Transfer.