▁re flow , ▁and ▁so ak ▁processes . ▁By ▁setting ▁P WI ▁values , ▁engine ers ▁can ▁ensure ▁that ▁the ▁re flow ▁sol der ing ▁work ▁does ▁not ▁over he at ▁or ▁cool ▁too ▁quickly . ▁ ▁Formula ▁ ▁The ▁Process ▁Window ▁Index ▁is ▁calculated ▁as ▁the ▁worst ▁case ▁( i . e . ▁highest ▁number ) ▁in ▁the ▁set ▁of ▁thermal ▁profile ▁data . ▁For ▁each ▁profile ▁stat istic ▁the ▁percentage ▁used ▁of ▁the ▁respective ▁process ▁window ▁is ▁calculated , ▁and ▁the ▁worst ▁case ▁( i . e . ▁highest ▁percentage ) ▁is ▁the ▁P WI . ▁ ▁For ▁example , ▁a ▁thermal ▁profile ▁with ▁three ▁therm oc ou ples , ▁with ▁four ▁profile ▁statistics ▁logged ▁for ▁each ▁therm oc ou ple , ▁would ▁have ▁a ▁set ▁of ▁twelve ▁statistics ▁for ▁that ▁thermal ▁profile . ▁In ▁this ▁case , ▁the ▁P WI ▁would ▁be ▁the ▁highest ▁value ▁among ▁the ▁twelve ▁percent ages ▁of ▁the ▁respective ▁process ▁windows . ▁▁ ▁The ▁formula ▁to ▁calculate ▁P WI ▁is : ▁▁▁▁ ▁where : ▁ ▁i ▁= ▁ 1 ▁to ▁N ▁( number ▁of ▁therm oc ou ples ) ▁ ▁j ▁= ▁ 1 ▁to ▁M ▁( number ▁of ▁statistics ▁per ▁therm oc ou ple ) ▁ ▁measured ▁value ▁[ i ,   j ] ▁= ▁the ▁[ i ,   j ] th ▁stat istic ' s ▁measured ▁value ▁ ▁average ▁limits ▁[ i ,   j ] ▁= ▁the ▁average ▁of ▁the ▁high ▁and ▁low ▁( spec ified ) ▁limits ▁of ▁the ▁[ i