This picture shows our group instrumenting the first 767 ever built (-001) for a full-scale ground vibration test. This was done just prior to first flight. We would mount over 100 low-frequency accelerometers all over the airplane. We then attached a large electromagnetic shaker to the airframe at different points. We would then excite the airframe, record the signals, and synthesize the mode shapes for the aircraft. They would use this data to calibrate the analytical models to predict what would happen in flight. I sat in the white trailer you can see in the right running test equipment to acquire the data and produce the test results.