ZERO IN ON

{v.} 1. To adjust a gun so that it will exactly hit (a target); aim at. * /Big guns were zeroed in on the enemy fort./ * /American missiles have been zeroed in on certain targets, to be fired if necessary./ 2. {slang} To give your full attention to. * /The Senate zeroed in on the Latin-American problems./ * /Let's zero in on grammar tonight./