[kh99]

Yeah, what squidsk said. I simplified the explanation a little, the code actually divides the unix time (seconds since Jan 1 1980 or something like that) by ten and checks that the remainder is 0, which happens when the last digit is 0 (since we're dividing by 10). But you can just as easily divide by 7 (or whatever) and check for a remainder of 0 to get a 1 in 7 chance.