(color online) Measurement of anisotropic upper critical fields exemplified by temperature dependence of resistivity for Rb₂Cr₃As₃ crystals under magnetic fields along (a) and perpendicular to (b) the crystallographic c axis. The resulting data are plotted in panel (c), yielding the superconducting phase diagrams (from Ref. [54]). The crossing between 4.5 K and 5 K comes from different samples (with slightly different T_c values) employed.