Update chapters/synchronous.tex

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

chapters/synchronous.tex

@@ -171,7 +171,7 @@ \section{Rationale for Clocked Semantics}\label{rationale-for-clocked-semantics}
   Clocked subsystems using arithmetic blocks are straightforward to optimize.
   When a standard math-block (e.g.\ addition) is part of a clocked sub-system it is automatically
   clocked and only evaluated when the clocked equations trigger.
-  For standard when-clauses one either need a separate sampled math-block for each operation, or
+  For standard when-clauses one either needs a separate sampled math-block for each operation, or
   it will conceputally be evaluated all the time.
   However, tools may perform a similar optimization for standard when-clauses
   and it is only relevant in large sampled systems.