The following is in acm_proc_article-sp.cls:
Code: Select all
\long\def\@makecaption#1#2{
\vskip \baselineskip
\setbox\@tempboxa\hbox{\textbf{#1: #2}}
\ifdim \wd\@tempboxa >\hsize % IF longer than one line:
\textbf{#1: #2}\par % THEN set as ordinary paragraph.
\else % ELSE center.
\hbox to\hsize{\hfil\box\@tempboxa\hfil}\par
\fi}