

This equation describes a two phase exponential decay. Y starts out equal to Span1+Span2+PLATEAU and decays to PLATEAU with fast and slow components. The two halflives are 0.6932/K1 and 0.6932/K2. In the figure, the two rate constants differ tenfold, but the spans were equal. The curve is not obviously biphasic, and it takes a very practiced eye to see that the curve does not follow a single phase model.