Function values can be read directly from the graph using the mouse, and reference marks can be added to individual plots in order to call attention to noteworthy features.

Reading the Graphics Display

1. Right click anywhere in the graph background to activate the global popup menu.
2. Select the Trace menu item. The mouse cursor changes to crosshairs and ordinate values are appended to all entries in the legend to the right of the graph. These are function values at the current [abscissa] location of the mouse cursor, which is recorded in a separate field inserted at the top of the legend when the Trace feature is activated. Ordinate and abscissa values are updated continuously as the mouse cursor is moved around the graphics display.
   If multiple functions are plotted, the value of each is recorded in the field to the right of its name in the legend.
   For functions of more than one variable, the mouse cursor is mapped to a unique set of coordinate values with the help of a projection plane. Specifically, the mouse screen location is projected onto a coordinate plane in the function space, and the projected point has coordinates that are recorded at the top of the legend. The projection plane is always normal to one of the coordinate axes, and intercepts that axis at a point on the coordinate grid. The placement of this plane (also called the trace plane) is fully editable using the buttons and spinner control found at the foot of the legend.

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Plot Markup – Annotations

1. Select the Trace item from the global popup menu; this places the display in reading mode (see above).
2. Double-click on a plot to annotate that plot (add markup) beneath the current location of the graphics cursor.
   For functions of one variable, plot annotations take the form of intersecting lines passing through the ordinate and abscissa values at the mouse location when the double click occured. For functions of two variables, the ordinate lines are replaced by coordinate planes; for functions of three variables the annotations are simply enlarged points in the function space.
   For a graph with multiple plots, markup affects only the top-most plot. Double-clicking on another plot brings that plot to the front, where it can be annotated with a second double-click.
   An annotation can be erased by following the same procedure, i.e., double-clicking on an existing annotation (can be difficult). A more reliable (and less frustrating!) erasure method is to right-click the mouse on the plot and select the Erase Annotation menu item from the popup menu.
3. Once created, an annotation can be 'tweaked' with the help of keyboard shortcuts.
   Hold down the alt key while pressing the left-right arrow keys to shift the annotation sideways relative to the screen. For functions of more than one variable, the alt key combined with the up-down arrow keys shifts the annotation vertically, while alt++ and alt+− move the annotation closer to or away from the screen, respectively.
4. Multiple annotations can be added to a single plot. In such cases, the aforementioned operations affect only the active annotation, distinguished by its brighter color. The key combination alt+tab cycles among all annotations, activating each in turn.

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