. ▁The ▁specification ▁limit ▁is ▁the ▁toler ance ▁allowed ▁for ▁the ▁process ▁and ▁may ▁be ▁statist ically ▁determined . ▁Indust ri ally , ▁these ▁specification ▁limits ▁are ▁known ▁as ▁the ▁process ▁window , ▁and ▁values ▁that ▁a ▁pl otted ▁inside ▁or ▁outside ▁this ▁window ▁are ▁known ▁as ▁the ▁process ▁window ▁index . ▁ ▁Using ▁P WI ▁values , ▁processes ▁can ▁be ▁accur ately ▁measured , ▁analyz ed , ▁compared , ▁and ▁track ed ▁at ▁the ▁same ▁level ▁of ▁statistical ▁process ▁control ▁and ▁quality ▁control ▁available ▁to ▁other ▁manufact uring ▁processes . ▁ ▁Statist ical ▁process ▁control ▁Process ▁cap ability ▁is ▁the ▁ability ▁of ▁a ▁process ▁to ▁produce ▁output ▁within ▁specified ▁limits . ▁ ▁To ▁help ▁determine ▁whether ▁a ▁manufact uring ▁or ▁business ▁process ▁is ▁in ▁a ▁state ▁of ▁statistical ▁control , ▁process ▁engine ers ▁use ▁control ▁charts , ▁which ▁help ▁to ▁predict ▁the ▁future ▁performance ▁of ▁the ▁process ▁based ▁on ▁the ▁current ▁process . ▁ ▁To ▁help ▁determine ▁the ▁cap ability ▁of ▁a ▁process , ▁statist ically ▁determined ▁upper ▁and ▁lower ▁limits ▁are ▁drawn ▁on ▁either ▁side ▁of ▁a ▁process ▁mean ▁on ▁the ▁control ▁chart . ▁The ▁control ▁limits ▁are ▁set ▁at ▁three ▁standard ▁devi ations ▁on ▁either ▁side ▁of ▁the ▁process ▁mean , ▁and ▁are ▁known ▁as ▁the ▁upper ▁control ▁limit ▁( U CL ) ▁and ▁lower ▁control ▁limit ▁( L CL ) ▁respectively . ▁If ▁the ▁process ▁data ▁pl otted ▁on ▁the ▁control ▁chart ▁remains ▁within ▁the ▁control ▁limits ▁over ▁an ▁extended ▁period , ▁then ▁the ▁process ▁is ▁said ▁to ▁be