No, they have varied. Some have been as long as 15 years; some have lasted for as little as five years. The feeling is that 10 years is about right, I think, from the government's point of view. It gives us sufficient certainty to plan ahead, but it also allows government to review what we do on a regular basis and to ensure we're still doing what parliamentarians feel we should do.
That, of course, is another advantage of having a charter. In the U.K., acts of Parliament are generally not time limited. Having a charter—which is time limited—does give parliamentarians the opportunity to review the BBC from time to time.