Sets or returns the error amount. The meaning of this value is dependent on the value of ErrorBar.ValueType.
If the ValueType is Custom, this property will return 0. Setting this property when the ValueType is custom will cause the ValueType to change to FixedValue.
If the ValueType is not Custom, then this property specifies the error in both the positive and negative direction. This may be a fixed (absolute) value, a percentage of the data point's value, or a standard deviation, depending on the ValueType.
If you create a new error bar using ExcelWriter, then the Value will have a default value of 2 for the 2007 Office file formats (.xlsx, .xlsm, etc), and a value of 0 for the 2003 Office file formats (.xls).