commands/Other-geometrical-parameters.md

@@ -59,6 +59,10 @@ Other geometrical parameters
 
   If `orientation` is combined with `stripangle` or `stripdir`, the latter are
   ignored.
+  
+  **NOTE**: If multiple `#dir` inputs are given, they must be orthogonal
+  directions. If the inner product between any pair of them is nonzero, an error
+  is raised.
 
   **NOTE**: With the option `orientation`, the program uses an alternative 
   construction method for the Hamiltonian, which may cause the time consumption