Reference 7721 S has chrome-plated case; silver dial and registers; matchstick hands

Reference 7721 N has chrome-plated case; black dial with white registers; matchstick hands

Reference 7721 SN has chrome-plated case; white dial with black registers; matchstick hands

Reference 7721 NT has chrome-plated case; black dial with white registers; tachymeter scale on dial; matchstick hands