Sets or returns the formula specifying the positive error value.
This formula should reference a range of cells that contains the values for the positive error. If there is only one cell referenced, then all data points will have a positive error equal to the value in that cell. If there are multiple cells referenced (e.g. A1:A5), then the first cell's value will be used for the positive error of the first data point, the second cell's value will be used for the second data point, and so on.
The positive error value represents the error in the positive direction. For example, if you have a data point at a Y position of 3.0, and the positive error value for the ErroyBarY is .5, then the error bar will extend from 3.0 (the data point) to 3.5 (the error value added to the data point). The CustomMinusFormula specifies the error going in the other direction.
Setting this property will cause the error bar to show its positive error if it was not already doing so, and will change the ValueType property to Custom.
By default error bars will use a FixedValue ValueType, and CustomPlusFormula will return an empty string.