2.1.1479 Part 4 Section 188.8.131.52, errDir (Error Bar Direction)
a. The standard does not define the behavior when the errDir element is omitted.
In Office, if this element is not defined the default behavior is x for horizontal bar charts. For all other chart types, the default behavior is y.
b. The standard states errDir can be a child of any errBars element.
Office loads and respects this element on any errBars parent element; however, this element is only saved back out on line or scatter series.