NFL -- Clock Errors Reviewable?

[DadofTwins]

I read recently that the NFL changed a rule about video replay being used to correct clock errors at the end of the half. Yesterday in the Baltimore-Indy game, the Colts ran a play with 9 seconds left on the clock. The pass was incomplete, but at the end of the play the clock still showed 7 seconds.

Watching at home, I timed the play from snap to whistle and came up with about 4 seconds for the play, which should have left 5 seconds (plus or minus one) on the clock. The difference turned out to be worth 4 points, as those two extra seconds gave the Colts time to run one more play before a FG try.

I don't have a dog in this hunt (watching the officials is far more entertaining than the game itself, anyway), and I'm not a football official myself (a guy can dream, I guess), but I am curious.

Is there somebody on the field whose job it is to make sure the clock operator starts and stops the clock correctly? Is the clock operator a league official, or is (s)he provided by the home team? And with the exception of the last play, is the clock ever reviewable?

Thanks.