▁stable . ▁▁ ▁The ▁toler ance ▁values ▁specified ▁by ▁the ▁end - user ▁are ▁known ▁as ▁specification ▁limits ▁– ▁the ▁upper ▁specification ▁limit ▁( US L ) ▁and ▁lower ▁specification ▁limit ▁( LS L ) ▁respectively . ▁If ▁the ▁process ▁data ▁pl otted ▁on ▁a ▁control ▁chart ▁remains ▁within ▁these ▁specification ▁limits , ▁then ▁the ▁process ▁is ▁considered ▁a ▁capable ▁process , ▁denoted ▁by ▁. ▁ ▁Man ufact uring ▁industry ▁has ▁developed ▁custom ized ▁specification ▁limits ▁known ▁as ▁Process ▁Windows . ▁ ▁Within ▁this ▁process ▁window , ▁values ▁are ▁pl otted . ▁The ▁values ▁relative ▁to ▁the ▁process ▁mean ▁of ▁the ▁window ▁are ▁known ▁as ▁the ▁Process ▁Window ▁Index . ▁By ▁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 . ▁ ▁P WI ▁in ▁electron ics ▁manufact uring ▁ ▁An ▁example ▁of ▁a ▁process ▁to ▁which ▁the ▁P WI ▁concept ▁may ▁be ▁applied ▁is ▁sol der ing . ▁ ▁In ▁sol der ing , ▁a ▁thermal ▁profile ▁is ▁the ▁set ▁of ▁time - temper ature ▁values ▁for ▁a ▁variety ▁of ▁processes ▁such ▁as ▁slope , ▁thermal ▁so ak , ▁re flow , ▁and ▁peak . ▁▁ ▁Each ▁thermal ▁profile ▁is ▁ranked ▁on ▁how ▁it ▁fits ▁in ▁a ▁process ▁window ▁( the ▁specification ▁or ▁toler ance ▁limit ). ▁Raw ▁temperature ▁values ▁are ▁normal ized ▁in ▁terms ▁of ▁a ▁percentage ▁relative ▁to ▁both ▁the ▁process ▁mean