I often conduct the acid demand test following my initial ph reading to obtain a "second" reading. If my initial reading looks like 7.4-7.7ish, one drop of 0005 should take it down .2. If my second reading looks more like color comparator 7.2-7.5, I know my initial reading was closer to either 7.4 or 7.8. I then add more or less acid depending on a comparison of both initial and second readings. I really don't know if this procedure is valid or necessary, but figure I am getting a second opinion, honing my skill at reading the comparator tube (as in, "I guess it was closer to 7.5 rather than 7.7") and I enjoy messing with reagents.