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The squared visibility
amplitude is estimated using
\[ V^2=\frac{}{^2},\]
where $X$ and $Y$ are the real and imaginary parts of the complex visibility
(derived by Fourier transform of the bin counts at the fringe frequency),
and $N$ is the total count rate (sum of the bin count rates). The brackets
denote average. We have left off a leading constant, which is related to
the reduction in amplitude due to the binning.
}
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