diff --git a/pt100/pt100.tex b/pt100/pt100.tex
index e7c6812..14ea229 100644
--- a/pt100/pt100.tex
+++ b/pt100/pt100.tex
@@ -193,7 +193,29 @@ Temperature range calculations and detailed calculations
 on the effects of each test case are found in section \ref{pt100range}
 and \ref{pt100temp}. 
 
-
+%\paragraph{Consideration of Resistor Tolerance}
+%
+%The separate sense lines ensure the voltage read over the PT100 thermistor are not
+%altered due to having to pass any significant current.
+%The PT100 element is a precision part and will be chosen for a specified accuracy/tolerance range.
+%One or other of the load resistors (the one we measure current over) should also
+%be of this accuracy.
+%
+%The \ohms{2k2} loading resistors may be ordinary, in that they would have a good temperature co-effecient
+%(typically $\leq \; 50(ppm)\Delta R \propto \Delta \oc $), and should be subjected to
+%a narrow temperature range anyway, being mounted on a PCB.
+%\glossary{{PCB}{Printed Circuit Board}}
+%To calculate the resistance of the PT100 element % (and thus derive its temperature),
+%having the voltage over it, we now need the current.
+%Lets use, for the sake of example $R_2$ to measure the current flowing in the temperature sensor loop.
+%As the voltage over $R_3$ is relative (a design feature to eliminate resistance effects of the cables).
+%We can calculate the current by reading
+%the voltage over the known resistor $R2$.\footnote{To calculate the resistance of the PT100 we need the current flowing though it.
+%We can determine this via ohms law applied to $R_2$, $V=IR$, $I=\frac{V}{R_2}$, 
+%and then using $I$, we can calculate $R_{3} = \frac{V_{R3}}{I}$.}
+%As these calculations are performed by ohms law, which is linear, the accuracy of the reading
+%will be determined by the accuracy of $R_2$ and $R_{3}$. It is reasonable to
+%take the mean square error of these accuracy figures.
 
 \subsection{Range and PT100 Calculations}
 \label{pt100temp}
@@ -249,6 +271,37 @@ for any single error (short or opening of any resistor) this bounds check
 will detect it.
 
 
+
+\paragraph{Consideration of Resistor Tolerance.}
+%
+The separate sense lines ensure the voltage read over the PT100 thermistor is not
+altered by to having to pass any significant current. The current is supplied 
+by separate wires and the resistance in those are effectively cancelled
+out by considering the voltage reading over $R_3$ to be relative.
+%
+The PT100 element is a precision part and will be chosen for a specified accuracy/tolerance range.
+One or other of the load resistors (the one we measure current over) should also
+be of this accuracy.
+%
+The \ohms{2k2} loading resistors should have a good temperature co-effecient
+(i.e. $\leq \; 50(ppm)\Delta R \propto \Delta \oc $).
+%
+To calculate the resistance of the PT100 element % (and thus derive its temperature),
+knowing $V_{R3}$  we now need the current flowing in the temperature sensor loop.
+%
+Lets use, for the sake of example $R_2$ to measure the current.
+%
+We can calculate the current $I$, by reading
+the voltage over the known resistor $R_2$ and using ohms law\footnote{To calculate the resistance of the PT100 we need the current flowing though it.
+We can determine this via ohms law applied to $R_2$, $V=IR$, $I=\frac{V}{R_2}$, 
+and then using $I$, we can calculate $R_{3} = \frac{V_{3}}{I}$.} and then use ohms law again to calculate
+the resistance of $R_3$.
+%
+As these calculations are performed by ohms law, the accuracy of the reading
+will be determined by the accuracy of $R_2$ and $R_{3}$. It is reasonable to
+take the mean square error of these accuracy figures.
+
+
 \section{Single Fault FMEA Analysis \\ of PT100 Four wire circuit}
 
 \subsection{Single Fault Modes as PLD}