Yep, the switch is SL-I or II... Didn't know it was for setting the K3 command in case of miss...
I've read that "Vozvrat" should be pressed if the target was missed or after time, and that makes me to think that self destruction is from some kind of iternal clock... Don't remember where, but also read thah NVA officers stopped that clock and achieved almost 80 km shot, which results on colateral damage on the ground... I was wonderning what "Vozvrat" exactly do?