▁through ▁the ▁dis ks ▁before ▁going ▁to ▁the ▁l amps . ▁The ▁advantage ▁of ▁this ▁was ▁that ▁there ▁was ▁nothing ▁that ▁had ▁to ▁be ▁done ▁to ▁the ▁setup ▁in ▁order ▁to ▁de ci pher ▁a ▁message ; ▁the ▁machine ▁was ▁" sym met rical " ▁at ▁all ▁times . ▁ ▁The ▁En igma ' s ▁reflect or ▁guaranteed ▁that ▁no ▁letter ▁could ▁be ▁en ci pher ed ▁as ▁itself , ▁so ▁an ▁A ▁could ▁never ▁turn ▁back ▁into ▁an ▁A . ▁This ▁helped ▁Polish ▁and , ▁later , ▁British ▁efforts ▁to ▁break ▁the ▁ci pher . ▁( See ▁C rypt analysis ▁of ▁the ▁En igma .) ▁ ▁Sch erb ius ▁joined ▁forces ▁with ▁a ▁mechanical ▁engineer ▁named ▁Ritter ▁and ▁formed ▁Ch iff ri erm as ch inen ▁AG ▁in ▁Berlin ▁before ▁demonstr ating ▁En igma ▁to ▁the ▁public ▁in ▁Bern ▁in ▁ 1 9 2 3 , ▁and ▁then ▁in ▁ 1 9 2 4 ▁at ▁the ▁World ▁Post al ▁Congress ▁in ▁Stockholm . ▁In ▁ 1 9 2 7 ▁Sch erb ius ▁bought ▁Koch ' s ▁pat ents , ▁and ▁in ▁ 1 9 2 8 ▁they ▁added ▁a ▁plug board , ▁essentially ▁a ▁non - rot ating ▁manually ▁re wire able ▁fourth ▁rot or , ▁on ▁the ▁front ▁of ▁the ▁machine . ▁After ▁the ▁death ▁of ▁Sch erb ius ▁in ▁ 1 9 2 9 , ▁Will i ▁K orn ▁was ▁in ▁charge ▁of ▁further ▁technical ▁development ▁of ▁En igma . ▁ ▁As ▁with ▁other ▁early ▁rot or ▁machine ▁efforts ,