You may drag any of the cacti to a desired height.
Click the "Setup" button to change the number and basic arrangement of the cacti.
Create, edit, and delete vertical markers by holding down the SHIFT key. With the SHIFT key held, click to create a marker anywhere. Or drag the top of an existing marker to move it. Or double-click on the top of a marker to delete it.
You can clear all the markers by clicking the Clear Markers button.