Flashbacks reveal how Finch created the machine in Person of Interest (9 p.m., CBS/Ch. 2).
Elsewhere on TV ...
The Biggest Loser (7 p.m., NBC/Ch. 5): Team competition ends; individual competition begins.
NCIS (7 p.m., CBS/Ch. 2): Dozens of children from military families come down with a mysterious illness.
NCIS: Los Angeles (8 p.m., CBS/Ch. 2): A senator's daughter is attacked.
The Voice (8 p.m., NBC/Ch. 5): A winner is declared in the season finale.
How Sherlock Changed the World (8 p.m., PBS/Ch. 7): How the methods of the fictinal character actually impacted crime investigators.