The two methods in question are:

  void set_draw_value (int draw_value)
  int get_draw_value () const

However, the GTK+ documentation says

  void gtk_scale_set_draw_value (GtkScale *scale, gboolean draw_value);

   Specifies whether the current value is displayed as a string next
   to the slider. 

so integer values doesn't make any sense. I'm attaching a patch for
correcting this - the patch also adds more documentation and fixes some of
the existing. I haven't documented calc_digits, though, since I'm not quite
sure what is is supposed to do.

The patch shouldn't cause any real API change because of the implicit
conversion rules between bool and int, but I guess it is important to
change before the ABI freeze. (Note that the patch hasn't been syntax
checked since I couldn't get the CVS version of gtkmm-1.3 to compile.)