I could never read my AP test kit... the color differences were just too subtle. I've also heard it's less then 100% accurate.
I've since purchased the seachem kit, and am pleased with it.
10 gallon 2.6 WPG
3 Dwarf Puffers, 3 Ghost Shrimp, 3 Otos
Planted with Java Fern, C. retrospiralis, Java moss, chistmas moss, L. repens, R. rotundifolia, Wisteria, C. wendtii, C. lucen, S. subulata, M. heterophyllum, C. carolina