Field help (USEQTY) 

This field indicates the consumed quantity.

If material tracking follows an operation tracking or production reporting, the quantity to be tracked is automatically indicated and cannot be modified.

This field is initialized for an initial tracking with the quantity planned in the work order.
This is only accessible if the filter submits the non-closed operations.
The modification of this quantity leads to a recalculation of the actual quantities proposed for the materials to be tracked.

The lines in red characters indicate that: