Being that I'm new to maintaining my own pool and haven't quite gotten the 'bug' for extreme accuracy, so here's how I'm doing it.
For me, simplicity is the key. I need to be able to eyeball it. I purchase those 2.5 gallon yellow chlorine jugs from the store. Each one of those is 320 oz which equals 80 oz x 4. I won't even bother adding chlorine to my pool unless it needs at least 1/4 jug, or 80 oz. Then, I'll only add chlorine rounded up to the nearest 1/4 jug. This way, it's fairly easy to eyball it and even if I'm over/off by a 1/4 jug, it won't have too much affect on things. Again, simplicity is key for me.
Also, I live in South Florida and have a LOT of evaporation and rain. This keeps things changing fast enough where being off by a 1/4 jug here or there wont have any lasting effects.
I hope I don't get slammed for what I just wrote.