A hand-timed 40 and a laser 40 on the same run are not the same number, and running more trials will not make them match. Studies put the gap at roughly 0.22 to 0.31 seconds [1, 2, 6]. Two separate problems cause it, and they stack. The person holding the stopwatch starts late and stops early, and separately, different timing setups start the clock at different moments, so the same run can produce different times. Electronic timing gates remove the human error from both ends and give you one number that repeats.
The stopwatch starts late and stops early
A 2010 study measured both ends of the error separately. The hand timer started the watch 0.065 seconds after the athlete's first movement, then stopped it 0.160 seconds before the athlete reached the line [3]. Hand times came out 3.99 percent faster, 5.23 seconds against 5.45.
The finish accounts for about 70 percent of that error. The difference between the two ends comes down to anticipation. A timer watching the athlete come at the finish line can see it coming and hits the button a moment early. Nobody can see the start coming, so the timer is reacting, and the watch goes late. Both errors shorten the recorded time, so they add up rather than cancel. And because they sit at the two ends of the run, they do not shrink when the run does. A hand-timed 10-yard split loses about the same number of seconds as a hand-timed 40.
Timing a split in the middle of a run is different, because the timer can see both ends coming and the two misses partly cancel. Across 25-meter mid-race splits the average error came out at only 0.04 seconds, but any single trial was still off by about 0.15 seconds [4]. Across seven hand timers on the same trial, the fastest and slowest stopwatches were about 0.19 seconds apart [5, 6].
Where the clock starts is the bigger variable
Two laser 40s can differ by more than a tenth on the same run, and it is not the laser [5]. Every timing setup has to pick the exact moment the clock starts. That is a decision somebody makes, and different setups decide differently.
The combine defines it as the hand leaving the ground [8]. A human watches for that and starts the watch, which is where roughly 0.06 seconds of late start creeps in [3]. OVR Sprint's In-Beam start catches that same moment automatically. Put the gate on the ground at the front line, set the athlete in a three-point stance with the down hand breaking the beam, and the clock fires the instant that hand lifts. That is the closest match to how a combine 40 is actually run, so use it any time the number is going to a recruiter.
Anything that starts the clock later reads faster. A gate at the line with the athlete set a foot behind it gives away the first few inches free [7], and the further back the athlete sets up, the faster the number gets [5]. Other start methods are worth using when they answer a different question, but they do not produce a combine-comparable 40.
Inside a program, which start you pick matters less than consistency does. A 40 earns most of its value compared against the same athlete's last 40, and any protocol run the same way every time will show that. Pick one and standardize the beam height, the start distance and the stance. A tenth off an athlete's own previous best is a real tenth whatever protocol produced it.
Protocols built on a run-up start and fixed splits avoid the problem, because the athlete is already at speed when the clock starts and nobody has to judge first movement.
What to add to a hand time
Add about a quarter second to a hand-timed 40. A 2015 study of 81 college football players found hand times 0.22 seconds faster with experienced timers and 0.26 faster with novices [1], and high school federation rules add a flat 0.24 seconds to any hand time [2]. An earlier study of 59 Division II players found a bigger gap, 0.31 seconds [6], so a quarter second is the low end of what studies report.
What to say when a recruiter compares your times
Say how the time was taken. A 5.15 on the laser is the same run as about a 4.90 on a stopwatch, and two 40s can be squared up that way. Benchmark tables are harder, because most of them do not say whether the times behind them were hand timed or gated.
Corrections are a patch. A single fixed number cannot absorb a spread that changes from trial to trial and timer to timer, and that spread is bigger than most of the improvement a coach is trying to see across a training block. The authors of that stopwatch study concluded the spread made a reliable correction factor impossible, and recommended reporting hand times without one [4]. Electronic timing gives a number that holds up without any adjustment, and it picks up real improvement a stopwatch would miss.
Sources
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- Validity and Reliability of Hand and Electronic Timing for 40-yd Sprint in College Football Players. Journal of Strength and Conditioning Research, 2015, 29(6):1509-1514. https://pubmed.ncbi.nlm.nih.gov/25785707/
- Hand Time Conversion Standards (NFHS and Track & Field News conversions). Athletic.net documentation. https://support.athletic.net/article/4sjokyho13-hand-time-conversion-standards
- Determining the Source of Temporal Differences Between Electronic and Hand Timing Systems in the 40 Yard Dash. Journal of Strength and Conditioning Research, 2010. https://journals.lww.com/nsca-jscr/abstract/2010/01001/determining_the_source_of_temporal_differences.69.aspx
- Reliability and Accuracy of Handheld Stopwatches Compared With Electronic Timing in Measuring Sprint Performance. Journal of Strength and Conditioning Research, 2008, 22(6):1969-1976. https://pubmed.ncbi.nlm.nih.gov/18978613/
- Sprint Running Performance Monitoring: Methodological and Practical Considerations. Sports Medicine, 2016, 46(5):641-656. https://link.springer.com/article/10.1007/s40279-015-0446-0
- Comparison Between Hand and Electronic Timing of 40-yd Dash Performance in College Football Players. Journal of Strength and Conditioning Research, 2010, PMID 20072055. https://pubmed.ncbi.nlm.nih.gov/20072055/
- A Buyer's Guide to Sports Timing for Speed. SimpliFaster. https://simplifaster.com/articles/buyers-guide-sports-timing/
- How Accurate Is the 40-Yard Dash at the NFL Combine? MileSplit. https://www.milesplit.com/articles/445650/how-accurate-is-the-40-yard-dash-at-the-nfl-combine
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