diff --git a/fmmd_concept/fmmd_concept.tex b/fmmd_concept/fmmd_concept.tex
index ff7a3fa..3d7c02f 100644
--- a/fmmd_concept/fmmd_concept.tex
+++ b/fmmd_concept/fmmd_concept.tex
@@ -254,7 +254,7 @@ of the Safety Integrity Levels (SIL) of EN61508 \cite{en61508}.
 \section{A wish list for a failure mode methodolgy}
 \begin{itemize}
 \item All component failure modes must be considered in the model.
-\item It should be easy to integrate mechanical, electronic and software models.
+\item It should be easy to integrate mechanical, electronic and software models \cite{sccs}[pp.287].
 \item It should be re-usable, in that commonly used modules can be re-used in other designs/projects.
 \item It should have a formal basis, that is to say, it should be able to produce mathematical proofs
 for its results.
diff --git a/introduction/introduction.tex b/introduction/introduction.tex
index 89b12fe..c96dc92 100644
--- a/introduction/introduction.tex
+++ b/introduction/introduction.tex
@@ -118,6 +118,11 @@ computing elements. A tragic example of the mechanical and electrical elements
 interfacing to a computer is found in the THERAC25 x-ray dosage machine.
 With no common notation to integrate the saftey analyis between the electrical/mechanical and computing
 domains, synchronisation errors occurred that were  in some cases fatal.
+The interfacing between the hardware and software for the THERAC-25 was not considered
+in the design phase.
+Niel Story in the formal methods chapter of "safety critical computer systems"
+describes the different formal languages suitable for hardward and software and 
+bemaons the fact that no single language is suitable for for such a broad range of tasks \cite{sccs}[pp. 287].
 
 \paragraph{Requirements for a rigorous FMEA process} 
 It was determined that any process to apply