Fig. 1.  The reduction in the concentration of a tracer substance (Hgb, hemoglobin) when a fixed amount of tracer is diluted by increasing amounts of water (A ). The correct proportion between Hgb concentration and water volume cannot be obtained by placing the baseline Hgb in the denominator (B ), but only by placing the diluted Hgb in the denominator of the ratio used to calculate dilution (C ).