Your summary function is updating when the record is committed. One way to commit a record is to click a blank area of the layout. You can add a script trigger to the field(s) being edited that performs a script that commits the record automatically and then they won't have to click. And in some cases, where the summary field is from a related table, an unstored calculation field in the layout's underlying table, instead of the related table can use an aggregate function such as Sum instead of the summary field to compute the same value without needing this extra step in order to get the field to update.
Thanks Phil...It worked wonderfully...