Pair-to-Pair measurements are used to measure one pair against another. Power Sum measurements select a pair and then measure the disturbances from other pairs within the same sheath. This can be used in a 4-Pair or other high pair count (25, 50, 100 and up) to determine the effects of all the cables (of course testers only test 4-Pair at a time). Power Sum ACR, ELFEXT, and bidirectional NEXT measurements are made with the LT8000 Series. In general, this results in an approximately 3-dB loss limit when compared to pair-to-pair test values.