CARuler

CARuler provides vertical and horizontal ruler classes designed to work with QwtPlot. You can create as many rulers as you like. During construction, the ruler gets attached to the plot. Thus, the plot takes ownership of all rulers known to it. Rulers are draggable and emit a signal when its position changes.
There is a built-in editing facility for ruler attributes in the form of a right click menu. It is also possible, through the right click menu, to lock any ruler in its current position or a specify a position in which it should be locked.