Aerospace physiologists calculate the g level by looking at the normal force that acts along the longitudinal axis of the pilot (z’ axis in figure 4). The number g’s is just the ratio of the normal force to the pilot weight. As the centrifuge rotates, the room where the pilot sit inside the gondola is free to roll outwards around the y’ axis. Figure 3(b) shows a cut-away that illustrates how the pilot’s orientation in the room changes in the gondola. Note that the C-arm attached to room is not directly connected to the straight arm shown in figure 3(a). It is drawn there to simply help visualize the motion. Figure 4 shows the coordinate axes and unit vectors.