--- loncom/html/adm/help/tex/Tolerance.tex	2002/07/18 15:52:27	1.2
+++ loncom/html/adm/help/tex/Tolerance.tex	2013/07/05 18:30:40	1.4
@@ -1,7 +1,7 @@
 \label{Tolerance}
 A \textbf{tolerance\index{tolerance}} parameter determines how closely
-the system will require the student's answer to be in order to count it correct.
-
+the system will require the student's answer to be in order to count it correct. 
+The tolerance parameter should always be defined for a numerical problem.
 
 For technical reasons, it is almost never a good idea to set this parameter
 to zero. Computers can only approximate computations involving real numbers. For instance,
@@ -15,17 +15,25 @@ to exactly match the computers idea of t
 default too large for some problems. 
 
 There are
-two kinds of tolerance. For some answer $a$ and a tolerance $t$,
+three kinds of tolerance. For some answer $A$ and a tolerance $T$,
 
 \begin{enumerate}
 \item an \textbf{Absolute} tolerance\index{absolute tolerance}\index{tolerance, absolute}
-will take anything in the range $a\pm t$. So if $a=10$ and $t=2$, then
+will take anything in the range $A\pm T$. So if $A=10$ and $T=2$, then
 anything between 8 and 12 is acceptable.
  Any number in the tolerance field \emph{without} a \textbf{\%} symbol is
 an absolute tolerance.
 \item a \textbf{Relative} tolerance\index{relative tolerance}\index{tolerance, relative}
-will take anything in the range $a\pm at$, where \emph{t} is interpreted
-as a percentage. Any number in the tolerance field \emph{followed by} a \textbf{\%}
+will take anything in the range $A\pm aT$, where \emph{T} is interpreted
+as a percentage/100. Any number in the tolerance field \emph{followed by} a \textbf{\%}
 symbol is a relative tolerance. For example, $a=10$ and $t=10\%$ will accept
 anything between 9 and 11. 
-\end{enumerate}
\ No newline at end of file
+
+\item a tolerance that is a calculated variable (identified by \$ sign as
+the first character). For example, if an answer is $\$X$,and for a student
+possible values range from $-\$X1$ to $+\$X1$, you could choose $T =
+\$tolerance = \$2X1/100;$ acceptable answers would then be from
+$\$X-\$tolerance$ to $\$X+\$tolerance$. (This is especially useful when answers
+close to zero are possible for some students)
+
+\end{enumerate}