Well, whether the pH is at 7.7, or more like 7.9...either way you add whatever amount of acid and then check it again in a few days. Then if it's 7.8 or geez maybe 8? Then you (or..whoever) will learn to round up or down to dose more or less. Each pool uses chems at different rates. You just don't want the pH getting way off. Stay in the 7s. If you have other concerns, like scaling, you'll adjust that, but that's when you've got the kit and a few rounds under your belt