What is the source of the ETC column on Task List Page?

Document ID : KB000103575
Last Modified Date : 27/06/2018
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The non labor ETC hours show up as expected on the Assignment list section on the Task Properties page. However, on the Task list page, they show up as 0. How does the ETC get updated on the Task list page?
The ETC amounts displayed on both the Gantt and Task list are aggregate values. 

Labor resources are hourly resources so their ETC (and Actuals) are measured in hours. 

While the non-labor resources are considered cost resources, the ETC (and Actuals) for these type of resources are typically measured in costs or units.

The way that the aggregation is done on the Task/Gantt list, only the hourly ETC (and Actuals) are taken into account. The non-labor resources are ignored as their ETC (and Actuals) are not measured in hours.