When the Michaelis-Menten equation is obeyed, the rate near the beginning of an enzyme-catalyzed reaction (or of an experiment on transport) can be found accurately from the slope of a chord joining two points on the progress curve. This slope gives the rate at an intermediate concentration. Exact values of this intermediate concentration are easily calculated from equations in the text, and a number of values have also been tabulated. Methods of using two chords to find the initial rate are given. A mid-point formula for numerical differentiation is advocated when the Michaelis-Menten equation does not hold.
