Of the factors that determine whether fluid moves from capillary blood into tissue or vice versa, capillary hydrostatic pressure is the only one that can change rapidly. Using this app a student or instructor can see how arterial and venous pressures and pre- and post-capillary resistances affect capillary pressure. Possible simulations include effects of a tourniquet, hemorrhagic hypotension, reflex vasoconstriction, etc. The app can be used for self-instruction or classroom demonstrations.