When I'm adding up several numeric fields, the sum is not always calculated correctly. In certain cases the value is shown as [Null] instead of as the actual sum.
To calculate the sum, I use the formula tool:
UnitsVolume_01_2015 + UnitsVolume_02_2015 + ...
Both input and output fields are formatted as double.
When I export the data to Excel and add up the same fields in Excel, sums are calculated correctly. I can't see any misformatted values, leading/trailing white spaces or any other obvious issues that could explain this odd behavior.
Any ideas why the sum could be [Null] instead of the actual value?