I've got a grid of entries, the two important columns are a tick box (required), and a time in hrs (hrs).

Where is the best method to recalculate the total hours (TxtNHours), in the click event method or the interactive change event?

My calculation code looks like this:

DODEFAULT()
SELECT SUM(hrs) as total FROM linemarkingbody WITH (buffering=.t.) WHERE linemarkingbody.no=linemarkinghead.no AND required INTO CURSOR tmptotal
IF ISNULL(TMPTOTAL.TOTAL)
 REPLACE totalhrs WITH 0 IN linemarkinghead
ELSE 
 REPLACE totalhrs WITH tmptotal.total IN linemarkinghead
ENDIF 
thisform.txtNHours.Refresh