Illustrations of the VSVPA effect with mock data. The top two panels show the mock data F356W, and the bottom two panels show F410M. The first row of each pair shows noise-free data, and the second row shows results with noise added. From left to right, panels show simulated epoch 1, simulated epoch 3, and the difference image. The difference image is smoothed with a 009 Gaussian as for the real data. All images are 15 across. The white cross marks the position of the varying point source. The arms of the cross are 006 end-to-end.