I want to make a special check on table data by trigger!

But I cannot use following commands as no difference.

Getfldstate() should return 2 if edit!
OldVal(Fieldname), CurVal(FieldName) should difference if change...

but at update trigger, everything gone correct!

I have tried both Buffer mode and not!
for buffer-mode, when tableupdate(), no different found!
for non-buffer-mode, of cos, no different!

How can I compare the value change is in acceptable range!?
it should include external change on it!