Microsoft project management software used to plan, manage, and communicate a project schedule and other information among workgroup members, project managers, and other stakeholders.
Damien Deffieux, you're right, it's not there. Seems like a reasonable thing that should be there, but why not is a mystery.
How are you plotting this, in MSP reports, or export (copy/paste) the data into excel and graph there?
It is easy to copy the baseline cost from the task usage view, paste in excel, make formula to cumulate, and graph.