How well can a quantum measurement pin down an unknown state?

Some quantum measurements are powerful enough to fully identify an unknown quantum state from their statistics alone — but not all IC measurements are equally good at this. This work introduces a rigorous way to score that power for qubit measurements, shows that the symmetric SIC measurement is the best among minimal options, and proves that a channel's ability to preserve this power is directly tied to how much coherence it always outputs — connecting two seemingly separate quantum resources.