Bit of a minor thread resuscitation here, but I was also reading that class feature and thought it seemed really oddly worded. If it only lasts for the one round, that makes the capstone ability (to use it multiple targets) functionally useless.
I’m thinking that maybe the intention is that the calibration lasts until you use the ability again, but the bonus is only added against the first attack from the targeted opponent each round. That lets the capstone actually do something and actually provides some benefits over just using a shield each round.