Writing in texmaker these lines
(the mount heigh is $1200m$).
we saw it in \ref{chapter1}.
width=6.02099737532808in (inside tikzpicture environment)
all the dots (fullstop) get replaced by this symbol

When I compile the document then it behaves like a dot, and get rendered as a dot/fullstop. Even if it's not a problem thou, I would like to understand what this symbol means and if it has some reason to exist...
Anyone has a clue?
EDIT:
Compilable version:
\documentclass{book}
\begin{document}
(the mount heigh is $1200m$).
we saw it in \ref{chapter1}.
\end{document}