A little more clarification based on past student misunderstandings

assignment/blackbox_testing.md

@@ -139,6 +139,11 @@ stack. For example:
         should be traceable to `Calculator.calculate()`'s  functional
         requirements (listed after the assignment instructions).
 
+        -   Do *not* use the "Postfix Calculator Functional Specification."
+            This system-level specification is included for context. Your
+            testing requirements need to trace to the "`Calculator.calculate()` 
+            Functional Specification."
+
     1.  Develop the rest of the test cases in your test suite.  The test cases
         should be traceable to the testing requirements.