The researchers explored different ways to measure how efficiently plants use water. They looked at water use efficiency, intrinsic water use efficiency, and the cost of water for plants to gain carbon. Out of these, the measure that links carbon gain with water use under changing conditions gave the best insights. By focusing on this measure, the researchers found a simpler and more accurate way to understand how plants balance their water use with the carbon they gain. This can help predict how plants will use water in different environments more effectively.