The Henderson equation is identical to the Henderson-Hasselbach equation. The Henderson equation is the simplest way for the clinician to tackle the diagnostic of acid base disorders. The knowledge of the compensatory responses and the drawing of the map describing the relationship between H+, PaCO2, HCO3-enables the clinician to make the diagnostic of single or dual acid base disorders very easily. Another step is made with the anion gap or the comparison of delta anion gap to the delta HCO3-concentration. The confrontation of these values with the Henderson equation or the map allows in some cases to make the diagnostic of triple disorders.