How tall are you? If someone measured you now, would it match your answer?
Measuring is never perfect. In Europe, height is measured in centimeters. In the US, in feet and inches (an inch is 2.54 cm, a foot is 12 inches). That means people in the US are measured with a less precise scale. It doesn’t matter though. No matter the scale used, height measurement is always an estimate. The goal is to get a ballpark figure.
Take the same approach when estimating the ROI of automation. Whether it’s time saved, errors reduced, or an increase in number of sales. First, figure out what it is that you want to measure. Then, give it a ballpark figure.
It will never be precise, and that’s not the goal. The key is to get a reasonable estimate that will guide your decision-making process.