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Calkulon

Practical

Stopwatch Timer

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Pro Tip

For accurate sports timing, the reaction time of the starter is often as significant as timer precision. Human reaction time averages 150–300ms — far greater than the ±10ms precision of most stopwatches.

Difficulty:Intermediate

Did you know?

The world's most accurate clock — an optical lattice clock — loses or gains less than 1 second in 30 billion years. For context, the universe is only 13.8 billion years old. These clocks are so accurate they can measure the difference in the flow of time between heights that differ by just 1 centimeter.

Mathematically verified
Reviewed May 2026
Used 46K+ times
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