What does the [@[bar foo]] operator do in Excel, in particular the at sign?
Solution 1:
The square brackets are used for structured references, which make it easier to reference data in named tables (which you can create by going to Insert → Table).
The @ is new notation in Excel 2010 replacing [#This Row] from Excel 2007. The at symbol is used to shorten formulas inside named tables referencing cells in the same row.
The inner square brackets are only needed because your bar foo table heading contains a space.