This dialog allows the modification of reference lines that have been created with the
* Add Reference Line...* command from the Graph Menu.
The dialog can be opened by double clicking on a reference line or by right clicking a selected
reference line and then choosing

A reference line has a non-empty name that can be used to identify it in the plot details dialog or in Python scrips.
The default generated names are: *line1*, *line2*, etc...

By default, a reference line is *Selectable*, meaning that it can be selected with the mouse
and also *Movable*, meaning that it can be dragged while pressing the left button of the mouse.
Reference lines, like any other object of a 2D plot layer, can be unselected by pressing the *ESC* key.

The drawing of the line can be disabled by unchecking the *Line* box.
This doesn't affect the drawing of the filling brush.

The area between a reference line and a baseline *Value* can be filled with a colored
brush if the *Fill to* group box is checked. The transparency of the filling brush can be
controlled using the *Opacity* slider. If the *Line* radio button from this
group box is checked, it is possible to choose an existing reference line in order to serve as baseline.
Of course, the two reference lines should have the same orientation (*Horizontal* or
*Vertical*).

Depending on the way in which the position of the line is defined,
there are two types of reference lines available in QtiPlot: *Value*-based and
*Statistics*-based lines.

The *Statistics*-based lines are attached to an existing plot curve and
can be displayed at any of the predefined statistical values from the list bellow. They are not *Movable*,
by default.

- Mean
Mean value of the curve data points.

- Median
Median value of the curve data points.

- Mean + Standard Deviation
Mean value plus the standard deviation of the curve data points.

- Mean - Standard Deviation
Mean value minus the standard deviation of the curve data points.

- Mean + Standard Error
Mean value plus the standard error of the curve data points.

- Mean - Standard Error
Mean value minus the standard error of the curve data points.

- Mean + 95% Confidence Interval
The upper limit of the 95% confidence interval for the mean of the curve data points.

- Mean - 95% Confidence Interval
The lower limit of the 95% confidence interval for the mean of the curve data points.

- Minimum
Minimum value of the curve data points.

- Maximum
Maximum value of the curve data points.

The 95% confidence interval for the mean is calculated as
Mean ± t_{0.975,n-1}SD/n^{1/2},
where n is the size of the data set (the number of data points of the plot curve), SD is the standard deviation and
t_{0.975,n-1} is the Student's t distribution with n - 1 degrees of freedom.

A reference line can be attached to an existing legend that can be selected from the
*Attach to* list when the *Label* group box is checked.
If there are no legends available in the plot layer you can create one by pressing the '+' button.
The button displays the text *New Legend* when hovered with the mouse.
The text of the newly created legend is set to *$(v, *6)*, which is the default
syntax for displaying the position of the reference line with six figures precision.

The attached legend may be edited by pressing the '...' button (displaying the text *Edit*
when hovered with the mouse). This opens the properties dialog of the selected legend.
When the properties dialog of the legend is closed, QtiPlot returns to the properties dialog of the reference line
(this dialog).

Only one coordinate of the position of the attached legend is controlled by QtiPlot. From the
*Alignment* list you may choose the anchor point of the legend: *Top*,
*Center* or *Bottom* if the reference line is horizontal and
*Left*, *Center* or *Right* if the reference line is vertical.
The other coordinate of the anchor point of the legend may be freely chosen, for example by moving the legend with
the mouse.