thanks, Rebecca for your reply.
i forgot to add that F1,F2 is actualy an example.
my need it to have a summery of a group of fields, thus F1,F2....Fn.
i have created a group (via document properties) and add all the fields i need (52)
and tried to sum(GroupName), or sum $(GroupName) or sum(<GroupName>)
but no luck.
can you assist?