Working Knowledge: Secret of Spin; March 2002; Scientific American Magazine; by Mark Fischetti; 2 Page(s)

For several generations now, people have experienced the same daily mystery as Scientific American reader Billy Ellis. "When I was opening my sports locker today," he writes, "it occurred to me that I have no idea how a standard combination lock works. I have been using them for decades. How does spinning the dial 'to the right, to the left, then to the right again' open the lock?"

The answer lies in ingenious yet simple design. Rotating the dial back and forth turns three internal disks. Each disk has a notch. When the notches align, the lock's shackle is freed. The combination for a standard lock from Master Lock consists of three numerals, one for each disk. A disk has 40 possible notch positions, so the dial has 40 numbers, which results in 64,000 potential combinations: 40 times 40 times 40.