Update chapters/classes.tex

Co-authored-by: Henrik Tidefelt <henrikt@wolfram.com>

chapters/classes.tex

@@ -354,7 +354,7 @@ \subsection{Component Variability Prefixes}\label{component-variability-prefixes
 The prefixes \lstinline!discrete!, \lstinline!parameter!, \lstinline!constant! of a component declaration are called \firstuse[variability!prefix]{variability prefixes}\index{component variability}\index{declared variability}\index{variability!declared|see{declared variability}} and define in which situation the variable values of a component are initialized (see \cref{events-and-synchronization} and \cref{initialization-initial-equation-and-initial-algorithm}) and when they are changed during simulation:
 \begin{itemize}
 \item
-  A variable \lstinline!vc! declared with \lstinline!constant!\indexinline{constant} prefix remains constant the simulation, with a value that is unaffected even by the initialization problem.
+  A variable \lstinline!vc! declared with \lstinline!constant!\indexinline{constant} prefix remains constant during simulation, with a value that is unaffected even by the initialization problem.
   This is called a \firstuse[---]{constant}, or \firstuse[constant!variable]{constant variable}\index{component variability!constant}.
 \item
   A variable \lstinline!vc! declared with the \lstinline!parameter!\indexinline{parameter} prefix has its value determined by the initialization problem, and has that value during the entire simulation.