In 2005, Jorge E Hirsch of UCSD published this paper in PNAS in which he put forward the h-index as a metric for measuring and comparing overall scientfic productivity of individual scientists. The h-index has been quickly adopted as the metric of choice for many committees and bodies.
The h-index (Hirsch Number) is a metric that is increasingly becoming of interest to researchers, especially in the light of the REF. An h-index is “a number that quantifies both the actual scientific productivity and the apparent scientific impact of a scientist“. You can work it out manually, but to be honest you’d need to be mad or a bibliometrics fiend to want to.