After blood pressure, perhaps the most important body biometric is your weight. And not just your overall weight, but how much of your body is fat. The Body Mass Index (BMI) is a very blunt instrument when it comes to estimating body fat; body type and amount of muscle make it a fairly inaccurate system. There are complex systems ranging from dual-energy X-ray absorptiometry (DXA) — which is the clinical gold standard — to specialized chambers designed to measure displaced air. And then there are weight scales and other devices that measure electrical currents passing through your body, and then estimate body fat and other tissue ratios.

Amazon also offers a system that is simple to use at home that will estimate your body fat. Amazon Halo owners who subscribe to the membership service ($4 per month) get access to the Body feature: a body composition app. You take a series of pictures using your smartphone, and the system uses them to create a 3D model of your body.

But how accurate can this be? A study by the  Pennington Biomedical Research Center at Louisiana State University tested the Halo system against DXA, smart scales, and other measurement approaches. They evaluated the body composition of 134 test subjects. In the end, Halo’s Body feature proved to be more accurate than all but the DXA, and its results were nearly as good.

Not only does the Body show you what your current body fat percentage is, it also provides a slider that lets you see how your body shape might change as your body fat percentage changes.

Information is the key to making lifestyle changes, and more accurate information should produce better results. The Body feature for Halo users could be a powerful tool in achieving weight loss.