zero in on
1. Aim precisely at a target, as in They zeroed in on the last snipers. [c. 1940]
2. Direct one's attention to, concentrate or focus on, as in We must zero in on the exact combination of ingredients, or The whole class zeroed in on the new assignment. This usage transfers aiming a firearm to directing one's attention. [Mid-1900s]
3. Converge on, close in on, as in The children zeroed in on the electric train display. [Mid-1900s]