Common Question 14

My graph has zero values in it but they are not being graphed. What is wrong?

ProEssentials include a Null-Data mechanism which consists of properties that define the Null-Data value for both YData and XData (the default value is zero). Anytime ProEssentials sees a data-point value equal to the Null-Data value, that data-point is ignored. The Null-Data value will not be graphed, tabled, or used in best-fit or statistical calculations.

NullDataValue defines the Null-Data value for YData.

NullDataValueX defines the Null-Data value for XData.

The Graph object only uses NullDataValue since it does not contain XData.

If your data has zero values that need to be graphed, you should set the Null-Data values to some other unexpected value, for example -9999. For the Scientific Graph, make sure to set both NullDataValue and NullDataValueX in order to graph zero values. Also, it is recommended to use a number like negative [-9999 or some other non-expected value] when using single precision storage because larger or more elaborate numbers sometimes have rounding problems.

Also take a look at Question 16. It may answer a common problem seen when changing the null data value.