2.1.1625 Part 4 Section 188.8.131.52, ST_BarDir (Bar Direction)
a. The standard states that each enumeration specifies that if the chart is a bar or column chart, the data markers are horizontal or vertical rectangles, respectively.
Office interprets each enumeration to specify that if the chart is a bar or column chart , the data markers are horizontally or vertically oriented. For 2D charts these are rectangles. For 3D charts, the shape is specified by the shape element.