My Macroeconmics book says about chain weighting -

Chain weighting. The US and many other countries, too now uses a method that's somewhere between fixed weight and xed-basket methods: chain-weighting. It mitigates some of the problems of applying the same prices over long periods of time (when relative prices often change dramatically), but doesn't eliminate them. If we told you exactly what it is, your eyes would glaze over. But trust us, it's an improvement.

 I read this and laughed out loud, and continued laughing, for five minutes. Something terrible has happened to my sense of humour.