The phrase `一板一眼` literally means “one strong beat, one weak beat.” This is the most basic and steady rhythm in Chinese opera music (a 2/4 time signature). Metaphorically, it was extended to describe a person or action that is just as regular, predictable, and strictly-patterned as this simple rhythm.
`一板一眼` is a common idiom used in both spoken and written Chinese. Its connotation is highly dependent on the context and the speaker's tone.