Candidates wary as opposition cameras roll 
- Video trackers have been used for at least 16 years in Mass., and the contest between Senator Scott Brown and Elizabeth Warren is no exception.
(GREG M. COOPER FOR THE BOSTON GLOBE)

Candidates wary as opposition cameras roll

- Video trackers have been used for at least 16 years in Mass., and the contest between Senator Scott Brown and Elizabeth Warren is no exception.

(GREG M. COOPER FOR THE BOSTON GLOBE)