String usage() {
        try {
            InputStream is = this.getClass().getResourceAsStream("/ngmf/ui/calc/Functions.txt");
            if (is == null) {
                return "";
            }
            int c;
            StringBuffer b = new StringBuffer();
            while ((c = is.read()) != -1) {
                b.append((char) c);
            }
            is.close();
            return b.toString();
        } catch (IOException ex) {
            return ex.getMessage();
        }
    }