diff --git a/fmmd_concept/fmmd_concept.tex b/fmmd_concept/fmmd_concept.tex
index 583556e..5f29b34 100644
--- a/fmmd_concept/fmmd_concept.tex
+++ b/fmmd_concept/fmmd_concept.tex
@@ -356,15 +356,16 @@ electronic components was published by the DOD
 in 1991 (MIL HDK 1991 \cite{mil1991}) and is a typical 
 source for MTFF data.
 %
-FMECA has a probability factor for a component error becoming % causing 
-a SYSTEM level error.
-This is termed the $\beta$ factor.
+FMECA has a probability factor for a component error occuring % causing 
+termed the $\alpha$ factor.
 %\footnote{for a given component failure mode there will be a $\beta$ value, the
 %probability that the component failure mode will cause a given SYSTEM failure}.
 %
-This lacks precision, or in other words, determinability prediction accuracy \cite{fafmea}, 
-as often the component failure mode cannot be proven to cause a SYSTEM level failure, but is
-assigned a probability $\beta$ factor by the design engineer. The use of  a $\beta$ factor
+A second probability factor, the liklihood that the component failure
+mode will cause a given SYSTEM failure, is termed the $\beta$ factor.
+As often the component failure mode cannot be proven to cause a SYSTEM level failure, but is
+assigned a heuristic probability $\beta$ factor by the design engineer. 
+The use of  a $\beta$ factor
 is often justified using Bayes theorem \cite{probstat}.
 %Also, it can miss combinations of failure modes that will cause SYSTEM level errors.
 %
@@ -387,8 +388,9 @@ Again this essentially produces a prioritised `to~do' list.
 \begin{itemize}
 \item Possibility to miss the effects of failure modes at SYSTEM level.
 \item Possibility to miss environmental affects.
-\item The $\beta$ factor is based on heuristics and does not reflect any rigorous calculations. Applying failure rates of individual components rather than individual failure modes
-makes the factor less statistically reliable.
+\item The $\beta$ factor is based on heuristics and typically does not reflect any rigorous calculations.
+\item The $\alpha$ factor is generally taken from lierature for generic component such as MIL~HDBK~\cite{mil1992}
+and may not take into account operational states and environemtnal factors.
 \item Complex component interaction effects can be missed.
 \item No possibility to model base component level double failure modes.
 \end{itemize}