John C. said:
Allow the user to select multiple items to show completion
of specified task concerning selected sample points.
I agree with Rick Brandt, insofar as I understand your description.
This is information that should be stored in a related table and
displayed in a subform. You could conceivably use code behind a single,
unbound combo box on the main form to add an entry to the related table
(and requery the subform) every time a selection is made in the combo
box, but that's a matter of user-interface design, not data structure.