diff --git a/fmmd_design_aide/fmmd_design_aide.tex b/fmmd_design_aide/fmmd_design_aide.tex
index 4a15f63..3b49759 100644
--- a/fmmd_design_aide/fmmd_design_aide.tex
+++ b/fmmd_design_aide/fmmd_design_aide.tex
@@ -165,7 +165,8 @@ Typically this type of circuit would be used to read a thermocouple
 and this erro symptom, "LOW READING" would mean our plant could 
 beleive that the temperature reading is lower than it actually is.
 To take an example from a K type thermocouple, the offset of 1.86mV
-from the potential divider represents amplified to $\approx \, 342mV$ would represent  $\approx \; 46\,^{\circ}{\rm C}$.
+from the potential divider represents amplified to 
+$\approx \, 342mV$ would represent  $\approx \; 46\,^{\circ}{\rm C}$.
 
 \clearpage
 \subsection{Undetected Failure Mode: Incorrect Reading}
@@ -181,14 +182,51 @@ allowance according to EN61508.
 
 \section{Proposed Checking Method}
 
-Were we to switch in a a second resistor in parrallel with the 
-safety resistor $R_{safety}$, using a switch (or transistor)
-we could detect the effect on the reading with the potential divider
+Were we to able to switch a second resistor in parrallel with the 
+safety resistor and switch it out again, we could tet 
+that it is still functioning correctly.
+
+With the new resistor switched in we would expect
+the voltage added by the potential divider
+to increase.
+
+The circuit in figure \ref{fig:mvamp2} shows an NPN transistor
+controlled by the `test line' connection, which can switch in the resitor R30
+also with a value of \ohms{2.2M}.
+
+We could detect the effect on the reading with the potential divider
 according to the following formula.
 
-\vspace{10pt}
-Work out a pot div formula, and some typical values
-\vspace{10pt}
+The potential divider is now $\frac{820R}{1M1+820R}$ over 5V this gives
+3.724mV, amplified by 184 this is 0.685V \adcten{140}.
+The potential divider with the second resistor
+switched out is $\frac{820R}{2M2+820R}$ over 5V gives 1.86mV,
+amplified by 184 gives 0.342V \adcten{70}.
+
+This is a difference of \adcten{70} in the readings.
+
+So periodically, perhaps even as frequently as once every few seconds
+we can apply the checking resistor and look for a corresponding
+change in the reading.
+
+Lets us analyse this in more detail to prove that we are indeed checking for
+the failure of the safety resistor, and that we are not instroducing
+any new problems.
+
+First let us look at the new transistor and resistor and 
+treat these as a functional group.
+In our analysis of the failure modes we have to consider
+both states of the transistor, ON and OFF.
+
+\begin{figure}[h]
+ \centering
+ \includegraphics[width=200pt,keepaspectratio=true]{./mv_opamp_circuit2.png}
+ % mv_opamp_circuit2.png: 577x479 pixel, 72dpi, 20.35x16.90 cm, bb=0 0 577 479
+ \caption{Amplifier with check circuit}
+ \label{fig:mvamp2}
+\end{figure}
+
+
 
 
 \section{FMMD analysis of Safety Addition}
diff --git a/fmmd_design_aide/mv_opamp_circuit2.png b/fmmd_design_aide/mv_opamp_circuit2.png
new file mode 100644
index 0000000..31150ef
Binary files /dev/null and b/fmmd_design_aide/mv_opamp_circuit2.png differ
diff --git a/symptom_ex_process/algorithm.tex b/symptom_ex_process/algorithm.tex
index eabea67..ab7f878 100644
--- a/symptom_ex_process/algorithm.tex
+++ b/symptom_ex_process/algorithm.tex
@@ -312,13 +312,14 @@ $$ atc(TC) = R $$
 \begin{algorithmic}[1]
  \STATE  { let r be a `test case result'}
  \STATE  { Let the function $Analyse : tc \rightarrow r $ } \COMMENT { This analysis is a human activity, examining the failure~modes in the test case and determining how the functional~group will fail under those conditions}
+ \FORALL { Environmental and Specific Conditions }
  \STATE  { $ R $ is a set of test case results $r_j \in R$ where the index $j$ corresponds to $tc_j \in TC$}
  \FORALL { $tc_j \in TC$ } 
      \STATE { $ rc_j = Analyse(tc_j) $} \COMMENT {this is Fault Mode Effects Analysis (FMEA) applied in the context of the functional group}
      %\STATE { $ rc_j \in R $ } \COMMENT{Add $rc_j$ to the set R}
      \STATE{ $ R := R \cup rc_j $ } \COMMENT{Add $rc_j$ to the set R}
    \ENDFOR 
-
+  \ENDFOR
   \RETURN $R$ 
 
 %\hline
diff --git a/symptom_ex_process/process.tex b/symptom_ex_process/process.tex
index 5f140d1..0776ee3 100644
--- a/symptom_ex_process/process.tex
+++ b/symptom_ex_process/process.tex
@@ -83,6 +83,8 @@ form `test cases'.
  \item Using the `test cases' as scenarios to examine the effects of component failures
 we determine failure~mode behaviour of the functional group. 
 This is a human process involving detailed analysis of the failure modes in the test case on the operation of the {\fg}.
+Where spcific environment conditions, or applied states are germane to the {\fg} these must be examined
+for each test case.
  \item Collect common~symptoms by determining which test cases produce the same fault symptoms {\em from the perspective of the functional~group}.
  \item The common~symptoms are now the fault mode behaviour of the {\fg}. i.e. given the {\fg} as a `black box' the symptoms are the ways in which it can fail.
  \item A new `derived component' can now be created where each common~symptom, or lone symptom is a failure~mode of this new component.