the 2 is 2% of the actual weight by volume, which you'll find when you study the test, as certainly label reading and comprehesion is #1 on every state test I've ever seen. 2 % is actually a fairly low percentage in the realm of iron concentrations, just about enough to stain up your sidewalks and driveway if you're careless. There are different types of iron sources as well, with some being more prone to being tied up in certain soil situations than others and some intended for quick foliar uptake and shorter lasting results. It's important that you learn the differences, not only between the different iron types, but the variations on the primary and secondary macro and micronutrient groups as well (muriates vs. sulfates, as an example). Otherwise, you're not designing a program, you're just buying some fertilizer.