An air traffic controller in the 1980s told me that the antiquated software that was then in use nationally approximated circles by polygons (dodecagons I think, though maybe octagons). There was a rule saying that two planes shouldn't be within a mile of each other, and the rule was supposed to enforced by software (so that some sort of alarm would go off if one plane was in the circular one-mile neighborhood of the other), but the software used a polygonal approximation to those circles, more precisely INSCRIBED circles, so it was possible for two planes to be slightly less than a mile apart without setting off the alarm. He told me that the controllers sometimes would arrange for this to happen for sport. Anyone know anything about this? My memory is unreliable, so I may have major details of the story wrong. Jim Propp