Top: spatial covariance Vϖ(θ) of parallax errors in the high-precision quasar sample. Red circles are the individual estimates, and thedashed black curve shows a fitted exponential. Bottom: same data for separations < 7° with errors bars (68% confidence intervals) and a running triangular mean (blue curve). The two highest points, for separations < 0.25°, are outside the plot in the top panel.
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