One measures how far you are from the centerline (the white line in the middle of the runway)
One measures how far away you are from the designated aiming point for landing (the blue box on the runway/two big chunky white boxes)
One measures how hard your landing was. If it went BAM it will get a big Feet Per Minute, and be bad. If it goes swooosh, it will get a low Feet Per Minute (Lower FPM = higher score, Higher FPM = lower score)
Then they are all added and then multiplied for your final score (not exactly sure how)
I think the precision variable combines center alignment with fore-aft measurements. The scores are based on precision, vertical speed, and rollout distance.