Bell homed in on the expected correlations of spin
measurements when shooting pairs of particles through the
device, while the detectors on either side were oriented at various
angles.
For thirty years, he had taken tens of thousands of
measurements of variously shaped surfaces moving at different
angles through the air using a «whirling arm,» a long pole that extended horizontally from a fixed vertical pole and spun at a preset velocity, a
device originally developed to test the flight of cannonballs.