This note points out some interesting aspects of a recent study of the flow resulting from the use of area change near the diaphragm of a shock tube. (1) Earlier studies (2,3) have been directed toward the use of area change for increasing the available shock speed, and thus have considered geometries where A4/A1 > 1 and A*/A1 = 1 [see notation on Fig. 1(a)]. In the current work, shock tubes with arbitrary values of these parameters are considered over the complete range of Ms (the shock Mach number).