The Style group box in the Styled Lines dialog controls the length of dashes and gaps in the line style.
The Preview Area at the bottom of the Styled Lines dialog displays the changes you make to the line. The Edit Area has a ruler (in pixels) to help you to size dashes and gaps. Each dash or gap can be selected and adjusted with its Slider.
The Style settings are:
Add Adds dashes or gaps. Set the length of the dashes or gaps with the numeric edit control or by clicking and dragging the sliders.
Delete Deletes the selected dash or gap. Select a dash or gap by clicking on its slider in the edit area.
Clear Removes all dashes and gaps.
Zoom Buttons Click to zoom the view of the edit area in or out.
Undo Click to undo previous changes made in the Style group box.
Grouping and Ungrouping Vector Objects
Positioning Vector Objects on the Canvas
Arranging Vector Object on the Canvas