Talk:Fencepost error

Millennia
VP: This article contains a fencepost error. Examine any ruler for the proper numbering: the leftmost post should be numbered 0. Same with birthdays: your birthdate is properly considered birthday 0, you then spend year 1 of your life awaiting birthday 1, and so on. The expression "the first inch" (or first mile) refers to the interval [0,1]; there is an obvious difference between being at the beginning and the end of the first inch.

The fact that most people celebrated the millennium at the beginning of 2000 instead of the end is a perfect example of an easily committed fencepost error. Oddly enough everyone manages to avoid this error for their own birthdays, celebrating their 10th birthday at the end of their tenth year, as they should, no doubt because they round down (reasonably enough, their exact age being a real number, not an integer) when giving their age as 9 during their 10th year. Had people considered the year 2000 to be Jesus' (moral) 2000th year, they would see more clearly that Jesus was 1999 during that year (beating Methusaleh by more than a millennium!) and would turn 2000 at the end of his 2000th year, melting the cake. (That Jesus' actual birthdate was a couple of years earlier is a red herring here.)

The numbering of the BC years is the mirror image of all this; the beginning of the first century BC was the start of the year 100 BC (so everyone receiving their year 100 BC calendar in the mail would correctly celebrate the turn of the century immediately), and Jesus' conventional birthdate (modulo the Dec 25-Jan 1 discrepancy) was at the end of the year 1 BC, which ooincided with the beginning of the year 1 AD. There is no year 0 BC or 0 AD, just as there is no zeroth lady in the White House (if we don't count Monica Lewinsky). Trying to "correct" this with any other numbering system is a failure to understand the existing system.


 * Nice try, but you overlook the fact that in a finite and non-circular situation, there is indeed one more post than there are fence segments. Any other way of numbering will not change that. &minus;Woodstone 16:04, 29 March 2006 (UTC)

Other errors
Why does this article mention musical chairs? I'm removing this paragraph pending further explanation:


 * Note that not all off-by-one errors are fencepost errors. The game of musical chairs involves a catastrophic off-by-one error where n people try to sit in n&minus;1 chairs, but this is not a fencepost error (see also pigeonhole principle). Fencepost errors come from counting things rather than the spaces between them, or vice versa, or by neglecting to consider whether one should count one or both ends of a row.

The game of musical chairs does not contain any error. The system is intentionally designed such that there will be one fewer chair than people. The pigeonhole principle isn't an issue of "mistake" either. ~ Booya Bazooka 06:06, 24 August 2006 (UTC)