Non-segmental platform devices can send electrical currents which help to analyze body composition to around the sternum, and then make an estimation of the top third of the body based on that measurement.  

A segmental device will calculate body composition for each individual body part, and also for a cross section of the entire body, the average of the total of these will then provide a full body composition analysis. This method allows for a more precise and accurate analysis of body composition as it includes less estimation.