You can create virtual objects on N'Gage platform which will use other objects as data source. This article explains how to use them. 

Virtual Meters

Virtual meters can be created directly within the Synoptic interface on the N'gage platform. These virtual meters allow you to aggregate data from various real meters present on the synoptic view. You can use the operators "+", "-", "*", and "/" to establish your formulas.

Once the virtual meter is created, you can retrieve the data generated by your formula just like any other meter in a Summary widget indicator by using the "@" symbol.

Virtual Sensors

Virtual sensors can be created directly within the Synoptic interface on the N'gage platform. These virtual sensors allow you to aggregate telemetered data from various real meters present on the synoptic view. You can use the operators "+", "-", "*", and "/" to establish your formulas.

Once the virtual sensor is created, you can retrieve the data generated by your formula just like any other meter in a Summary widget indicator by using the "@" symbol.