Plot of expected visibility amplitude as a function of baseline length for two frames of Model B230. Symbols show the noiseless visibility amplitudes that would be obtained if the source structure were frozen near minimum (black) and maximum (color) flux in the hot spot orbit. At maximum flux, points are color-coded and labeled by baseline as in Figure 3. Visibility amplitude falls off rapidly with baseline length, and the fractional variability on long baselines can be significantly different than that seen at zero spacing.