Tim Brown with a new (metaphorical) term to describe a value that can fluctuate between two set values:
In canal and river navigation, a lock is a device used for raising and lowering vessels between stretches of water that are at different levels. That’s exactly what our formula accomplishes. Our formula is a CSS calc “lock”.
To fluctuate between a 1.3em and 1.5em line-height depending on the screen width: