On 15 September 1938, most German nets stopped encrypting the doubled key with a common setting (the ground setting). The Poles had been able to take advantage of all messages in a net using the same machine settings to encrypt the doubled key. Now most nets stopped doing that; instead, the operator would choose his own ground setting and send it in the clear to the recipient. This change frustrated the grill method and the cyclometer card catalog. One net, the "Sicherheitsdienst" (SD) net, continued to use a common ground setting, and that net was used to reverse engineer new rotors (IV and V) that were introduced. The SD net traffic was doubly encoded, so the ANX method would not work. The grill method would sometimes fail after the Germans increased the number of plugboard connections to ten on 1 January 1939. When the SD net switched to the new message-key protocol on 1 July 1939, the grill method (and the cyclometer method) were no longer useful.