▁according ▁to ▁normal ▁En igma ▁rules , ▁except ▁that ▁an ▁active ▁pin ▁at ▁the ▁reading ▁station ▁for ▁a ▁pin ▁wheel ▁prevent ed ▁the ▁couple d ▁rot or ▁from ▁ste pping . ▁The ▁cycle ▁for ▁a ▁normal ▁En igma ▁was ▁ 1 7 , 5 7 6 ▁characters . ▁When ▁the ▁Schl üss el ger ät ▁ 3 9 ▁was ▁correctly ▁configured , ▁its ▁cycle ▁length ▁was ▁ ▁characters , ▁which ▁was ▁more ▁that ▁ 1 5 , 0 0 0 ▁times ▁longer ▁than ▁a ▁standard ▁En igma . ▁ ▁The ▁Schl üss el ger ät ▁ 3 9 ▁was ▁fully ▁automatic , ▁in ▁that ▁when ▁a ▁key ▁was ▁pressed , ▁the ▁plain ▁and ▁ci pher ▁letters ▁were ▁printed ▁on ▁separate ▁paper ▁t apes , ▁divided ▁into ▁five - digit ▁groups . ▁The ▁Schl üss el ger ät ▁ 3 9 ▁was ▁abandoned ▁by ▁German ▁forces ▁in ▁favour ▁of ▁the ▁Schl üss el ger ät ▁ 4 1 . ▁ ▁Techn ical ▁description ▁ ▁Note : ▁Otto ▁B ugg isch ▁gave ▁the ▁technical ▁description ▁of ▁the ▁ci pher ▁unit ▁as ▁part ▁of ▁T IC OM ▁home work . ▁ ▁Ger ät ▁ 3 9 ▁is ▁an ▁elect r ically ▁operated ▁ci pher ▁machine . ▁The ▁ci pher ▁technique ▁is ▁derived ▁from ▁the ▁En igma ▁ci pher ▁machine . ▁A ▁direct ▁current ▁passes ▁through ▁ 3 ▁or ▁ 4 ▁whe els , ▁with ▁ 2 6 ▁positions , ▁I , ▁II , ▁II , ▁a ▁reflect or ▁wheel ▁U , ▁and ▁the ▁again ▁through ▁the