A rigid scale is attached to the torsional chair (with its internal coil spring attached to provide a countering force). An arbitrary force (measured by the spring scale) can be exerted at an arbitrary angle (measured by the protractor) at an arbitrary distance from the center of the chair (measured by the scale) to produce some arbitrary rotation of the chair against its restoring spring. Equal torques can be applied in several different ways, or torques can be scaled by changing one or more of the variables. Measurements are good to about ten percent.
The photographs above show the chair being rotated about 180 degrees by an external torque, which is created by a force perpendicular to the radius vector (center) or at an angle of 45 gegrees with respect to the radius vector (right).
Note that this demonstration and demonstrations B2-22 and B2-32 use many of the same components.