Positions for about 3,900 asteroid were computed for every 6 hours in a given year for those reaching V = 16 or brighter. For a given asteroid and date, its position was compared against the position on the same date/time for the remaining asteroids.
If an initial approach within 0.5° was found, the perturbed positions for both asteroids were computed at 1-minute intervals ±4 hours of the initial time of closest approach. The date/time of the closest approach within the 481 positions was adopted.
Calculations by Brian D. Warner.