diff --git a/fmmdset/fmmdset.tex b/fmmdset/fmmdset.tex
index cdd134c..2d55ac7 100644
--- a/fmmdset/fmmdset.tex
+++ b/fmmdset/fmmdset.tex
@@ -96,7 +96,7 @@ From the point of view of fault analysis, we are not interested in the component
 For this study a {\fg} will mean a collection of components.
 In order to determine the symptoms or failure modes of a {\fg}
 we need to consider all failure modes of its components.
-By analysing the fault behaviour of a `functional group' with respect these failure modes
+By analysing the fault behaviour of a `{\fg}' with respect these failure modes
 we can derive a new set of possible failure modes.
 %
 This new set of faults is the set of derived faults from the perspective of the {\fg}, and is thus at a higher level of 
@@ -105,10 +105,10 @@ fault~mode abstraction. Thus we can say that the {\fg} as an entity, can fail in
 In other words we have taken a {\fg}, and analysed how it can fail according to the failure modes of its parts.
 These new failure~modes are derived failure modes.
 %The ways in which the module can fail now becomes a new set of fault modes, the fault~modes
-%being derived from the functional~group. 
+%being derived from the {\fg}. 
 We can now create a new `{\dc}' which has
-the failure symptoms of the functional~group as its set of failure modes.
-This new derived~component is at a higher failure mode abstraction
+the failure symptoms of the {\fg} as its set of failure modes.
+This new {\dc} is at a higher failure mode abstraction
 level than the {\bcs}.
 %What this means is the `fault~symptoms' of the module have been derived.
 %
@@ -390,7 +390,7 @@ via the RS232 serial line.
 
 This has a number of obvious {\fgs}, the PCB power supply, the milli-volt amplifiers,
 the analog to digital conversion circuitry, the micro processor and the UART (serial link - RS232 transceiver).
-It would make sense when analysing this system to take each one of these functional~groups in turn and examine them closely.
+It would make sense when analysing this system to take each one of these {\fgs} in turn and examine them closely.
 
 It would be sensible if the system could detect the most obvious fault~modes  by self testing.
 When these have been examined and diagnostic safeguard strategies have been thought up,
diff --git a/introduction/introduction.tex b/introduction/introduction.tex
index 3c3454d..d7a2f15 100644
--- a/introduction/introduction.tex
+++ b/introduction/introduction.tex
@@ -491,8 +491,16 @@ This element of FTA is discussed in \ref{surveysc}
 
 \section{Therac 25}
 
+The therac-25 was a computer controlled radiation therapy machine, which 
+overdosed 6 people between 1985 and 1987.
+An earlier computerised version of the therac-25 (the therac-20) used the same software but kept the 
+hardware interlocks from the previous manual operation machines. The hardware interlocks
+on the therac-20 functioned correctly and the faulty software in it caused no accidents.
+A safety study for the device, using Fault Tree Analysis% \cite{nucfta} 
+carried out in 1983
+excluded the software \cite{safeware}[App. A].
+
 
-\cite{safeware}[App. A]
 
 %% Here need more detail of what therac 25 was and roughly how it failed
 %% with refs to nancy