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They're called "instant reruns" by the networks, and now these encore presentations can be counted in a new way by Nielsen Media Research.

NBC is the first network to utilize a new system by Nielsen that will allow some of its programming to have both the original airdate and the encore aired later in the same week included in a single ratings report, rather than two separate reports. The first show to utilize this new system is "Heroes," which premiered Monday night and will have an encore run Saturday. Instead of two separate ratings, NBC has opted for one single one that will include viewers from both airings.

"As the growth of digital platforms and other viewing options emerge, Nielsen is unifying the reporting and processing of all national ratings and developing methods to support the wider array of choices open to all national program providers," Nielsen said in a release.

The ratings will not include duplicate viewing, and only add new viewers from the re-broadcast. But because of the system, final ratings for "Heroes" won't be available to advertisers, networks and the viewing public until Oct. 2 when Saturday numbers are typically released.

To be included in the system, the networks have to specifically request it, and then they have to meet a number of criteria, including identical national commercial and program content between the first airing and the encore airing.

Nielsen is the main ratings house that provides viewership numbers to the major networks and a host of regional television outlets.