The hydraulics power a frame that holds modules of various sizes and load-carrying capabilities (foam density and thickness). The modules can be easily swapped.
Once the measurements have been taken, a conventional-looking chair is produced from those measurements.
This project went bust in the recession of 1981-82. Perhaps this explains my undying hatred for Paul Volker and his monstrous economic ideas.
The whole explanation for how this works can be found can be seen at: http://elegant-technology.com/VFTROU.html
Just follow the links under the "Sitting Pretty" section. If you merely want to see the measuring chair in action: http://elegant-technology.com/resource/264/07_Sitting_fitting_264.mov "Remember the I35W bridge--who needs terrorists when there are Republicans"