The number of protesters in London on Saturday has been estimated anywhere from 250,000 to 500,000. So is it possible to count?
No one knows exactly how many people joined the march and rally against spending cuts.
As the march finished in Hyde Park, the Trades Union Congress, which organised the event, estimated there was about 250,000.
On the following day, they were saying it was between 400,000 and 500,000. So how do they count?
"It's an inexact science, which is why we're not making any very, very accurate claims," says Nigel Stanley, head of TUC campaigns.
"We have been piecing together information from yesterday and think we're close to half a million people."
http://www.bbc.co.uk/news/magazine-12879582
Note: Update Record, 28 March 2011 Last updated at 10:53 GMT