English: Skylab's Body Mass Measurement chair, the facility of the Body Mass Measurement experiment (M172), is shown here in this 1970 photograph. The M172 experiment determined the body mass of each crew member and observed changes in body masses during flight. Knowledge of exact body mass variations throughout the flight in significantly aided in the correlation of other medical data obtained during the flight. Mass measurements under zero-gravity conditions were achieved by the application of Newton's second law (force equals mass times acceleration). The Marshall Space Flight Center had program management responsibility for the development of Skylab hardware and experiments.