# Example 7.32: Add reference lines to a plot; fine control of tick marks

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Sometimes it’s useful to plot regular reference lines along with the data. For a time-series plot, this can show when critical values are reached in a clearer way than simple tick marks.As an example, we revisit the empirical CDF plot shown in Example 7.11. If you missed that entry, the data can be downloaded so you can easily explore the code shown below. We’ll show how to add a regular grid
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