function get_base_font_size()
{
    global $g_font_size;
    for ($i = 0; $i < count($g_font_size); $i++) {
        $unit = value::unit_from_string($g_font_size[$i]);
        if ($unit != UNIT_EX && $unit != UNIT_EM) {
            $font_size = units2pt($g_font_size[$i]);
            for ($j = $i - 1; $j >= 0; $j--) {
                $font_size = units2pt($g_font_size[$j], $font_size);
            }
            return $font_size;
        }
    }
    return 0;
}