MinorUnit Property
Returns or sets the minor units on the axis. Read/write Double.
Remarks
Setting this property sets the MinorUnitIsAuto property to False.
Use the TickMarkSpacing property to set tick mark spacing on the category axis.
Example
This example sets the major and minor units for the value axis in Chart1.
With Charts("Chart1").Axes(xlValue)
.MajorUnit = 100
.MinorUnit = 20
End With