How Do You Know When You Need to Change Your Color?

In the lab, you had RGB and like, I think it was seven points to a stop. So if your negative was a stop over instead of printing at 27 or whatever, some people printed at 25. If you were at 34, you knew your negative had twice the amount of light that the normal negative would have. It's got another seven points, which is another stop, which is double the light and so forth. And then you could look at the three color numbers and you could tell which color was spiking and which wasn't.