The equation is:
The constant, 1.36, is the amount of oxygen (ml at 1 atmosphere) bound per gram of hemoglobin. The exact value of this constant varies from 1.34 to 1.39, depending on the reference and the way it is derived. The constant 0.0031 represents the amount of oxygen dissolved in plasma at 1 atmosphere. The dissolved oxygen term generally can be ignored, but becomes significant at high pressures -- as in a hyperbaric chamber.