This is a convenience function to visualize the calibration ranges in a plot generated by
iso_plot_data with a gray area behind the data points. Note that
iso_evaluate_calibration_range must have been called at an earlier point to establish calibration ranges for different terms. Also note that if one of the chosen dimensions (x or y) is not part of the available calibration range for a panel but the other dimension is, it simply shows two lines bracketing the samples in the dimension that is part of the calibration range.
iso_mark_calibration_range(p, calibration = last_calibration(p$data))
a plot generated by