Asteroid-PPM Appluses
Asteroid positions were computed for every 0.25d in a given year and then compared against the position in the PPM (Positions and Proper Motions) Catalog.

If an initial approach within 0.5° was found, the position of the asteroid was recalculated using numerical integration once an hour for 12h on either side of the initial "hit". Interpolation was used to find the exact date and time of minimum distance.

Calculations by Brian D. Warner.