So, according to the graph, SGA's core audience was 1.25 million in its final season while SGU's core audience this season is 1.00 million. So, the core audience is down by about a quarter million, not the 2 or 3 million that Saquist suggests.
ETA: Actually, that chart is inaccurate too, at least for SGU ratings for this season. SGU was consistently right near 1 million, sometimes slightly above, some times slightly below. The chart shows SGU as always being being below 1 million, sometimes significantly below 1 million. I'm not sure how much I trust that chart now.
Mr Awe
The chart is accurate, but it shows the Syfy HH coverage ratings and not viewers in millions. See here:
http://forums.sgusucks.com/showthread.php/133-Ratings
There are more overviews on the site and also this information:
Live + SD Ratings
SGU, season 1 average: 1.684 million viewers
SGU, 1. half average: 1.949 million viewers
SGU, 2. half average: 1.445 million viewers
SGU, season 2 average: 1.078 million viewers (ep. 21 - 30)
In comparison to SGA's live + SD numbers:
SGA, 2. half of season 4 average: 1.7 million viewers
SGA, season 5 average: 1.610 million viewers
SGA, 2. half of season 5 average : 1.68 million viewers
Live + 7 Ratings
SGU, season 1 average: 2.29 million viewers (not including episode 18 and 19)
SGU, 1. half average: 2.54 million viewers
SGU, 2. half average: 2.01 million viewers (not including episode 18 and 19)
SGU, season 2 average: 1.556 million viewers (ep. 21 - 28)
In comparison to SGA's live + 7 numbers:
SGA season 1: 2.8 million viewers
SGA season 2: 2.2 million viewers
SGA season 3: 1.9 million viewers
SGA season 4: 2.0 million viewers
SGA season 5: 2.103 million viewers
*Season 1 was live + SD, since live + 7 did not exist yet*
SGA live + 7 ratings of the last 10 episodes of season 5:
The Lost Tribe - 2.5 million viewers
Outsiders - 2.0 million viewers
Inquisition - 1.9 million viewers
The Prodigal - 2.0 million viewers
Remnants - 2.2 million viewers
Brainstorm - 2.2 million viewers
Infection - 2.0 million viewers
Identity - 2.0 million viewers
Vegas - 2.3 million viewers
Enemy at the Gate - 2.5 million viewers