2.1.1570 Part 1 Section 21.2.2.226, valAx (Value Axis)

a.   The standard does place any restrictions on the val attribute of the axId child element.

Office requires that the val attribute of the axId child element match the val attribute of an axId element in the parent chart.

b.   The standard does place any restrictions on the val attribute of the crossAx child element.

Office requires that the val attribute of the crossAx child element matches the val attribute of an axId element in the parent chart.