What do food health star ratings actually tell us about nutrition?

Health star ratings on packaged food and drink were introduced 10 years ago, as a voluntary measure by the food industry.They’re supposed to rate the nutritional value of those foods, but when some highly processed cereals get 4 out of 5 stars, consumers could be misled into thinking they're making healthy choices.The federal government is currently preparing to make the system mandatory if the food industry doesn’t incorporate health star ratings on 70 per cent of all packaged foods by next year.But is the rating system the best way to work out the nutritional value of foods?