Returns or sets the base unit for the specified category axis Read/write XlTimeUnit
XlTimeUnit can be one of these XlTimeUnit constants.
expression Required. An expression that returns one of the objects in the Applies To list.
Setting this property has no visible effect if the CategoryType property for the specified axis is set to xlCategoryScale. The set value is retained, however, and takes effect when the CategoryType property is set to xlTimeScale.
You cannot set this property for a value axis.
This example sets the category axis on the chart to use a time scale, with months as the base unit.
.CategoryType = xlTimeScale
.BaseUnit = xlMonths