A comparison of continuous wave reflection scanning acoustic microscope (cwSAM) with conventional pulse-echo scanning acoustic microscope (PESAM) and continuous wave ultrasonic interferometer (cwUI) shows that the latter two are special cases of cwSAM. This comparison is followed to develop a theory for the V(z) of a cwSAM. Numerically evaluated continuous wave-V(z) [cw-V(z)] for an elastically isotropic specimen is compared with an experimental cw-V(z) obtained at the same frequency. It is shown that the dominant features of experimental cw-V(z), the standing waves between the lens and the sample in water and the Rayleigh surface waves at the interface of water and sample can be reproduced in the theoretical model. Determination of Rayleigh wave velocity and the velocity of sound in the coupling fluid are discussed. It is also shown that the equation for cw-V(z) can be reduced to the cwUI equation under conditions relevant to it.