>I have to sum all child records each time the user changes row or column in the grid. The child records are not saved yet. They may have changed the Qty or Price, or added or deleted a record, so I need to update the total as they navigate around in the grid. I do not save the records until the user has entered them all and clicks the Save button.
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>The let's them see the total before saving.
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Use SUM command as Chris suggested.

SUM to lnTotal for myParentFK = myGridAlas.myPK in grid's ARCC.