We recently reported that Cambridge physicist Stephen Hawking had the biggest one in the UK ( Times Higher , August 26). But we have since learnt that, in fact, Cambridge astronomer Martin Rees, soon to be president of the Royal Society, has a larger one still. H-index, that is - a measure of the impact of a scientist developed by Jorge Hirsch at the University of California, San Diego. Although Professor Hawking measured 62, Professor Rees scores 73. So now you know.