Also, 40 yd dashes are usually hand-timed, not electronic (not sure if it's done electronically at the combine, but I know each team hand times it anyway). The general rule in track is if your race is hand-timed, add .24 to it to get the electronic time. Thus, a lot of "4.3s" would be 4.5s electronically. The fact that Bolt ran what would calculate to be a 4.34 electronic time means that handtimed, we're looking at 4.1 for his 40.