Tuesday was another night of landmark ratings for the broadcast networks — and not in a good way. A number of shows sank to all-time lows in the key 18-49 demo, based on Nielsen overnights.

TVbytheNumbers.com reports that NBC’s “Smash” continued to push its way into uncharted low ratings territory, sinking to a series-worst 0.7 in viewers 18-49 to finish a distant third in a three-horse race at 10 p.m. The show fell 22% from last week’s 0.9.

Elsewhere on NBC, a fresh installment of “Betty White’s Off Their Rockers” managed a 1.1 in the 18-49 demo — one-tenth better than the repeat episode that kicked off prime time, but down 15% from a week ago. “Go On” equaled last week’s all-time low of 1.1, while “The New Normal” fell 10% to a 0.9, also matching its all-time low.

NBC wasn’t the only broadcast network looking at grim numbers. ABC’s entire prime-time lineup set or equaled historic lows, with “Celebrity Wife Swap” the best of the bunch with a 1.5 in 18-49, down a hefty 38% from last week’s premiere and a series low. “The Taste” fell 14% to an all-time-low 1.2, while “Body of Proof” matched last week’s historic low with a 1.2.

CBS saw all three of its dramas slip from a week earlier, with “NCIS” down 3% to a 3.3 in adults 18-49, “NCIS: Los Angeles” off 3% to a 2.8 and “Golden Boy” slipping 11% to a 1.6.

Fox won the night with a 3.4 in 18-49 for its two-hour “American Idol,” airing outside its usual Wednesday-Thursday pattern. The number was down 13% from last Wednesday.

Fox’s 3.4 average for prime time overall led the way in the 18-49 demo, followed by CBS (2.6 average), Univision (1.8), ABC (1.3) and NBC (0.9). CBS won total viewers with an average of 15.2 million, ahead of Fox (11.5 million), ABC (4.6 million), Univision (4.3 million) and NBC (3.0 million).