How to update master row when detail is changed

[M]

I have a grid which is set up for master/detail rows.

One or two of the fields in the master row displays fields based on the sum of fields in the detail rows. This is all working nicely, but I need to be able to update the information displayed in the master row when the detail is changed.

I'd rather not resort to refreshing the entire grid when somebody adds or deletes a new details row.

I know I can grab the master row data using the detailInit event, but how can I update this data and make the grid display the new data?

Thanks