A calculated value for the concentration of angiotensin II (AngII), the octapeptide, Asp-Arg-Val-Tyr-Ile-His-Pro-Phe, that is derived from angiotensinogen and acts as a powerful vasopressor and stimulator of aldosterone secretion, at which the energy produced by the active reduction in the diameter of a blood vessel in response to the application of AngII is halfway between the baseline value and the highest achievable value of such AngII-induced contractile energy.