Modern PALs are really clever. Basically, some minute random amounts of explosives are removed from each block under each detonator, and it only can be compensa

Modern PALs are really clever. Basically, some minute random amounts of explosives are removed from each block under each detonator, and it only can be compensated by corresponding adjustments of detonators firing timings. The correct timing offsets can be only produced by attaching an external device (PAL controller) to the bomb or warhead or launch console, and entering the arming code, which changes every 24 hours (it decrypts the timing offsets). Without the correct sequence, the device will fail to produce the proper nuclear explosion.