As far as I know you will have to use a 'big' if statment to see if the value of each check box is true. If all are tru ethen update the caption of your text field (assuming you are using a text field)
Say you have five check boxes. You could do a sum of the five check boxes and if they are all selected then they should add up to a negative 5. Here is a simple test...
Code:
If Me.Check1 + Me.Check2 + Me.Check3 + Me.Check4 + Me.Check5 = -5 Then
MsgBox "= -5"
Else
MsgBox "<> -5"
End If