Concentration is an ability used by Samus to replenish Missiles and Energy. Samus can use this ability at any time by standing still uninterrupted for a time. This will completely replenish Missiles to full. Concentration can also restore partial Energy in emergincy situations, but this takes more time. E-Recovery Tank allow concentration to be activated sooner and restore more Energy. This ability replaced the energy units of previous games used to heal Samus.