I am building a single axis tracking solar array rack using angle as part of the structure. In calculating deflection and stress I find that there is a max. and min. section modulus for angle metal, and on another site I found the following: "For unsymmetrical sections (T-beam for example) the section modulus used will differ depending on whether the compression occurs in the web or flange of the section." I can predict which parts of the rack will put the flange under compression or tension, but the statement doesn't state clearly whether one uses the maximum section modulus or the minimum section modulus for calculations when the flange is under compression, it simply states that it "depends." Which is it, please?