Nielsen Media Research has pledged to look again at a ratings rule change that has permitted NBC to massage the figures for one of its top-rated shows.

NBC has taken advantage of a double-dip rule whereby it can add unduplicated viewer numbers from Saturday's Heroes re-run to the total from Monday's first-run episode - effectively boosting the programme's standing in the weekly ratings ranker.

The move has been criticised by other broadcasters who have sent scathing comments to Nielsen, urging the ratings measurement body to re-evaluate the rule.

"We are reviewing those comments," a spokesperson for Nielsen Media Research confirmed.