The cryptanalyst hypothesised one plugboard interconnection for the bombe to test. Rejewski did it without knowing the plugboard permutation or the rotor wirings. British codebreakers succeeded in breaking these machines, which lacked a plugboard. The plugboard connections were known to the cryptanalysts as Stecker values. Each letter on the plugboard had two jacks. Keys were easily changed by changing the rotor disks and the plugboard wires. Like the British Colossus, it was programmed by plugboard and switches. This was useful in working out plugboard settings when a possible solution was being examined. The grill method also determined the plugboard wiring. The presence of a plugboard ("Steckerbrett") substantially increased the security of the encipherment. The plugboard allowed less specialized conditions to be imposed. The only remaining secret was the plugboard permutation. The plugboard contributed more cryptographic strength than an extra rotor. In addition, ten leads were used on the plugboard leaving only six letters unsteckered. Good operating procedures, properly enforced, would have made the plugboard Enigma machine unbreakable.