The intricate details of the initial flaw shape can be ignored in the first approximation, expecially since, upon incipient growth, the crack rapidly attains a stable configuration (normally semicircular, semielliptic, etc., depending on the stress distribution). Figure 3 shows an extrapolation of the macroscopic crack length record, a=f(N), over the life span preceding the macroscopic observations, down to a semicircular initial flaw length shown at the start of the cycling curve. Note that this is merely for illustration as the extrapolated X axis in Fig. 3 is not to scale. A median curve drawn through the macroscopic * crack growth record, a-f(N) with a>0.1 in., was differentiated graphically yielding da/d7V =/,(#) =/2(AA), which can be plotted against the corresponding AK levels given by