Controls can be bound, unbound, or calculated. A bound control is tied to a field in an underlying table or query. You use bound controls to display, enter, and update values from fields in your database. An unbound control doesn't have a data source. You can use unbound controls to display information, lines, rectangles, and pictures. The following illustration shows examples of bound, unbound, and calculated controls. A calculated control uses an expression as its source of data. An expression can use data from a field in an underlying table or query of a form or report, or from another control on the form or report.