I have been using the pool calculator for a couple months now and have some questions. I am curious as to why the volume seems to be higher than when I calculate it myself using the following formula: L x W x D x 5.9 (5.9 is the multiplier for oval pools that I have seen on a vast majority of sites). My calcuations come to 12' x 18' x 4' x 5.9 = 5,097.6 whereas the pool calculator equates it as 5500 gallons. What is the formula that the calculator uses and which is more accurate? Will 400 gallons make any difference in accurately testing and adding chemicals? I also have a question about the goals and target numbers. Reading the info on the calculator and a few of the earlier responses, it seems that the target level is the minimum level that I should have for the particular level I am testing for, correct? If so, then why does the goal have a bottom number lower than the target number? Should I strive to have the levels at a number in the middle of the goal? Also, the TA goal on the calculator for my pool is 70 - 90+ using the TFP choice in the dropdown at the bottom. What's with the plus? Does that mean I can have it higher or should I keep it at about 80? My prior Taylor test kit and I think my pool and/or heater manual suggest 80 - 120. Thanks.