ABSTRACT: Diffraction resulting from small scale ``turbulence'' in the intervening plasma acts as a filter on the visibility function of Sgr A*. This filter is strongly frequency dependent owing to the index of refraction law of cold plasma. Observations of nearby OH masers are similarly filtered. The asymmetry of the resultant apparent images of Sgr A* and the OH masers has been interpreted in terms of asymmetric ``turbulence'' resulting from magnetic pressure dominating plasma and turbulent pressures. The steady march of VLBI observations from cm to mm wavelengths has been directed toward evading the effects of diffraction. The possible mm/submm ``bump'' in the spectrum can mean that when good resolution is obtained at these wavelengths, we will be looking at a different source than that which produces the cm spectrum. Resolution of the cm spectrum will take a flyby in some future millenium! The 17-y VLA proper motion study of Backer & Sramek includes observations at both 6 cm and at 3.4 cm wavelengths. The precision is significantly smaller than the diameter of the diffractive image. Comparison of the two VLA results as well as Reid's VLBA result at 7 mm places stringent limits on refractive effects in the intervening plasma.