Dropping to a season low this late into a season is not good news for most shows. But then again, most shows aren't "Smallville."

The Superman series earned a 2.3 rating/4 share, according to Fast National ratings from Nielsen Media Research, an 11.5 percent drop from last week. But with a Stability Index Rating of 90.5 -- higher than every genre show except "Lost," which just premiered for the season -- the show's not sweating too much.

In fact, "Smallville" also is just 11.5 percent off its average with this week's showing, and is only 20.7 percent off its season high of a 2.9 household rating, far better than the difference for the best- and worst-performing episodes for many other shows.

The Stability Index Rating, by the way, is a comparison of the show's highest overnight rating versus its average, as collected by Airlock Alpha.

"Smallville," after 13 episodes, has still done much better than expected for The CW this season. It's low this week is still 9.5 percent better than last year's low for "Smallville," which clocked in at 2.1/4 en route to a 2.6/4 average, the same average "Smallville" has to this point a little more than midway through the season.

"Supernatural" continues to struggle, however. The show managed just an estimated 1.8/3, according to Zap2it, matching last week's estimated audience, and losing nearly 22 percent from its "Smallville" lead-in.

There was no special "CSI" leading into "Eleventh Hour" on CBS Thursday night, so that show came back down to Earth with a more manageable 7.9/13 to win the 10 p.m. hour, despite being down more than 18 percent from the previous week. It also lost nearly 25 percent of its lead-in audience from "CSI."

That rating was just enough to give "Eleventh Hour" yet another win among genre shows for the week, beating "Fringe" on Fox by more than 11 percent. The two-hour premiere of "Lost" finished third with a 6.6/10 average, followed by "Knight Rider" on NBC, "Smallville" and "Supernatural."

Fast Nationals usually provide a snapshot of what Americans are watching by pulling numbers from the top urban markets that includes both live viewing and same-day timeshifted viewing. A rating point generally represents more than 1.1 million households while the share indicates the percentage of televisions turned on that was tuned to the specific program. These numbers typically shift when final ratings are issued.

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