2.1.1458 Part 4 Section 188.8.131.52, builtInUnit (Built in Display Unit Value)
a. The standard states that the default value of the val attribute is thousands.
Office treats the default as a custUnit with a val attribute equal to 1.
This note applies to the following products: 2007, 2007 SP1, 2007 SP2.
b. The standard states that the builtInUnit element specifies that the display unit is one of the built in values.
In Office, this element specifies the display unit for the axis and also the text shown by sibling element dispUnitsLbl when the dispUnitLbl does not contain a tx child element.