Math is hard. Apparently

[madbaker]

2010 is the start of a new year. It is not the start of a new decade. Nor was 2000 the start of a new millennium. You start a new cycle with year 1, not year 0.

To pre-empt the "If that's how people use it, it's correct" argument, I offer this riddle:

Q: "How many legs does a dog have if you call a tail a leg?"
A: "Four. Calling a tail a leg does not make it one."

What I'm reading: Ken Scholes, Canticle

Comments

[madbaker.livejournal.com]

But then you get into the confusing issue where 10 decades do not coincide with a century.
In bond terminology, going from a price of 99 to a price of 100 is known as a "change of handle". Going from 2009 to 2010 is a change of handle but it's not a change of decade. Except as noted above where a change of decade is a continuous (and therefore meaningless for any precision) process.
Barbie's Dictum: Math is Hard.

[aimeric.livejournal.com]

"But then you get into the confusing issue where 10 decades do not coincide with a century."

Again, it depends. One century is 100 years, therefore 10 decades.

If you say 20th century AD, then they consist of 1901-1910, 1911-1920, ..., 1991 - 2000.

If you say "the 1900's", then they consist of the 00's, the teens, the twenties, the thirties (1930 - 1939), etc. Again, 10 decades in one century, but this is not the same as the 20th century AD (1900 is not part of the 20th century; nor is 2000 part of the 1900's).

All of which still comes down to what is meant when someone says "the last year of this decade". By itself, it's meaningless unless you establish the context. Though we'd probably agree that this is probably shorthand for "the last year of the 1st decade of the 21st century AD"...in which case your original gripe is absolutely correct.

My problem is that the current AD numbering system is confusing, since, as you've pointed out, in our current system, "change of Decade AD" != "change of handle". But if one were to change/create a new system using xxx0 - xxx9, one runs into thorny issues when trying to address the years around 10BC - 10AD. (is there a year 0? If so, which Decade is it in? Or is it in *two* different Decades [-9 to 0, 0 to 9]? Or neither?)

The current system has the virtue of being symmetrical around the pivot point, but you lose a year, so time calculation is a little annoying: while Jan 1 1AD to 5AD is 4 years, Jan 1 2BC to 5AD is 6 years, not 7. Plus the annoying non-change-of-handle-vs-decade issue.

Personally, I'd prefer using C-type remainders: a decade begins if (year mod 10) == 0. So -10 to 1 is a decade, as is 0 to 9. In this system, a decade always begins in a year that ends in a 0.

True, under this scheme, "change of handle == change of decade" only if the year is >=0. But anyone dealing with BC has to deal with odd calculations anyway (see above), as does anyone who has to deal with the 11-day jump in the 1582 Gregorian calendar. I'd rather have the asychronicity if it most calculations easier. If there's no simple uniform solution in engineering, it's often advantageous to make the common case fast rather than introduce a general solution with greater complexity.

Still, regardless of any scheme I'd prefer, it does annoy me that many people don't understand the current scheme. Which is probably a very long, roundabout way of saying that I agree with you :)