Cook 5 medium potatoes in jackets; peel and cube. Pour 1/4 cup low calorie French Salad dressing over warm potatoes; chill 2 hours. Add 1 cup chopped celery, 1/3 cup chopped onion, 4 hard cooked eggs, sliced, and 1 teaspoon salt. Combine 1/2 cup low calorie mayonnaise and 2 teaspoons prepared mustard; carefully mix with potato mixture. Add 1 teaspoon celery seed, if desired. Chill 4 hours. Makes 8 servings.