Closes #2180

Clarified Real Clock constructor interval argument.

chapters/synchronous.tex

@@ -444,8 +444,9 @@ \section{Clock Constructors}\doublelabel{clock-constructors}
 \textbf{Clock with Real Interval}\\
 
 The input argument, \lstinline!interval!, is a clocked Component Expression (see
-\autoref{argument-restrictions-component-expression}) or a parameter expression of type \textbf{Real} with
-min=0.0 and unit ``s''. The output argument is of base type Clock that
+\autoref{argument-restrictions-component-expression}) or a parameter expression.
+Interval must be strictly positive (\lstinline!interval>0.0!) of type \textbf{Real} unit ``s''. 
+The output argument is of base type Clock that
 ticks when time becomes t\textsubscript{start},
 t\textsubscript{start}+interval1,
 t\textsubscript{start}+interval1+interval2, ... The clock starts at the