Jim,

I don't think waterbear is telling you not to use the pool calculator, rather saying "proceed with caution." If you can reasonably estimate the volume of your pool (there is an estimating tool at the bottom of the calculator) and you know how the different chemicals react with one another (i.e. trichlor raises CYA and chlorine, but is acidic and lowers pH), it is a useful tool to use. I find myself mainly using the pool calculator for doses of bleach and borax.