▁II ▁and ▁II ▁are ▁known , ▁the ▁w iring ▁of ▁the ▁reflect or ▁wheel ▁and ▁the ▁pin ▁arrangement ▁of ▁N 1 ▁N 2 ▁N 3 ▁can ▁be ▁found ▁out ▁from ▁a ▁c rib ▁of ▁ 2 5 ▁letters , ▁this ▁was ▁a ▁fairly ▁labor ious ▁process . ▁▁ ▁If ▁the ▁inner ▁w iring ▁of ▁whe els ▁I , ▁I ▁and ▁II ▁and ▁of ▁the ▁reflect or ▁wheel ▁U ▁is ▁known , ▁it ▁is ▁like wise ▁possible ▁to ▁find ▁out ▁the ▁clear ▁message - setting ▁and ▁the ▁pin - arr ang ement ▁of ▁N 1 ▁N 2 ▁and ▁N 3 ▁from ▁a ▁c rib ▁of ▁ 2 5 ▁letters ; ▁this ▁too ▁is ▁a ▁labor ious ▁process . ▁ ▁The ▁above - ment ioned ▁weak ness ▁of ▁model ▁a ) ▁were ▁elimin ated ▁by ▁the ▁introduction ▁of ▁ste ck ering ▁and ▁adjust able ▁rings ▁of ▁model ▁b ), ▁although ▁this ▁had ▁been ▁done ▁primarily ▁for ▁quite ▁a ▁different ▁reason , ▁namely ▁to ▁make ▁inter change able ▁working ▁with ▁En igma ▁possible . ▁It ▁was ▁not ▁now ▁thought ▁that ▁there ▁was ▁any ▁longer ▁a ▁serious ▁possibility ▁of ▁a ▁break - in . ▁As ▁however ▁the ▁system ▁of ▁I ▁and ▁N 1 ▁still ▁had ▁a ▁relatively ▁small ▁period ▁of ▁ 2 1 ▁x ▁ 2 6 ▁it ▁appeared ▁des irable ▁to ▁destroy ▁this ▁too . ▁This ▁was ▁done ▁on ▁model ▁c ) ▁by ▁making ▁III ▁react ▁to ▁I , ▁and ▁presented ▁no ▁technical ▁difficulties . ▁ ▁Finally ▁in ▁model ▁c ), ▁the ▁total ▁number ▁of ▁periods