Conversation so far:
who has the fastest 40 yard dash ever
John Ross broke the 40-yard dash combine record with 4.22 at NFL Scouting Combine.
Who before John Ross had the fastest 40 yard dash ever?
Chris Johnson registered a time of 4.24 seconds and broke the all-time mark set by Rondel Menendez, his record was later broken by John Ross.

Question: How is the event timed?
Self-contained rewrite: How is the 40 yard dash timed?