[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./