It uses volume and weight measurements. Volume measurements are comparable to water weighing, which calculates the overall body fat through predictive models. We use similar predictive models to calculate the body fat of specific parts of the body.
There are several scientific research that correlates the precision of the model to DXA scans measurements.
Read some papers on scientific research below!
Clinical anthropometrics and body composition from 3D whole-body surface scans - NG B K, Hinton B J, Fran B, Kanaya A M, Sheperd J A - European of Clinical Nutrition
Predictive equations for central obesity via anthropometrics, stereovision imaging, and MRI in adults - Lee J J, Freeland-Graves J H, Pepper M R, Yao M, and Xu B - The University of Texas, Austin
Validation of a 3-dimensional photonic scanner for the measurement of body volumes, dimensions, and percentage body fat - Wang J, Gallagher D, Thornton J C, Yu W, Horlick M, and Pi-Sunyer F X - American Journal of Clinical Nutrition