Project Financials Management - Unplanned Cost

Summary:

In Project Financial Management, under Manage Project Budget, there are different versions getting displayed. On the top we have overview section/layout in which it gives high-level details of Budget, Budget to Date, Spent & Unplanned Cost etc. I would like to know how those figures are getting updated & what is the base. Can someone please clarify & give a detailed explanation of figures for Spent & Unplanned Cost? Please find the below screenshot for one of the projects

for your reference.

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