+ SCM table = get_pango_font_table (layout);
+ SCM sizes = scm_hash_ref (table, descr, SCM_EOL);
+ SCM size_key = scm_from_double (factor);
+ SCM handle = scm_assoc (size_key, sizes);
+ if (scm_is_pair (handle))
+ return unsmob_metrics (scm_cdr (handle));