A Gantt chart is a special type of horizontal bar chart. This type of chart depicts the elements in a project, and shows the project's work-breakdown structure. This enables every stakeholder to see a detailed representation of the project's status at a glance. Project managers frequently use a variety of software products to produce Gantt charts. Gantt charts are widely used because they are so useful for giving both detailed information and the project status big picture. The challenge, however, has been that until now Gantt charts have only been able to show a project's status at some particular time in the past. Progress made and costs incurred since the last chart update were always left to "best guesses."