By all accounts, this has been an even competition. The snaps have been distributed evenly. Locker went through a rough stretch a week ago, but he's had some high moments as well. Hasselbeck is the veteran, but he's made more mistakes overall.
John Glennon of The Tennessean notes that Hasselbeck's interceptions have piled up. He's thrown eight picks during team drills while Locker has thrown only two interceptions. This doesn't mean Locker necessarily is winning the battle, but it's a more meaningful stat than daily updates on completion percentage.
The coaches are certainly charting interceptions and a whole lot more. It's a stat that has added up over two weeks of practice rather than a small snapshot. Hasselbeck generally takes a lot of chances for a veteran in the regular season, too.