# Stopwatch

(c) Ansgar Koreng / CC BY-SA 4.0
A mechanical stopwatch
Sped-up stopwatch animation. The text below the image shows the time that corresponds to the movement of the indicator around the stopwatch.

A stopwatch is a timepiece designed to measure the amount of time that elapses between its activation and deactivation.

A large digital version of a stopwatch designed for viewing at a distance, as in a sports stadium, is called a stop clock. In manual timing, the clock is started and stopped by a person pressing a button. In fully automatic time, both starting and stopping are triggered automatically, by sensors. The timing functions are traditionally controlled by two buttons on the case. Pressing the top button starts the timer running, and pressing the button a second time stops it, leaving the elapsed time displayed. A press of the second button then resets the stopwatch to zero. The second button is also used to record split times or lap times. When the split time button is pressed while the watch is running it allows the elapsed time to that point to be read, but the watch mechanism continues running to record total elapsed time. Pressing the split button a second time allows the watch to resume display of total time.

Mechanical stopwatches are powered by a mainspring, which must be wound up by turning the knurled knob at the top of the stopwatch.

Digital electronic stopwatches are available which, due to their crystal oscillator timing element, are much more accurate than mechanical timepieces. Because they contain a microchip, they often include date and time-of-day functions as well. Some may have a connector for external sensors, allowing the stopwatch to be triggered by external events, thus measuring elapsed time far more accurately than is possible by pressing the buttons with one's finger. Stopwatches that count by 1/100 of a second are commonly mistaken as counting milliseconds, rather than centiseconds. The first digital timer used in organized sports was the Digitimer, developed by Cox Electronic Systems, Inc. of Salt Lake City Utah (1962).[1] It utilized a Nixie-tube readout and provided a resolution of 1/1000 second. Its first use was in ski racing but was later used by the World University Games in Moscow, Russia, the U.S. NCAA, and in the Olympic trials.

The device is used when time periods must be measured precisely and with a minimum of complications. Laboratory experiments and sporting events like sprints are good examples.

The stopwatch function is also present as an additional function of many electronic devices such as wristwatches, cell phones, portable music players, and computers.

## Human error on using stopwatch

Even though stopwatches are created to be more accurate, humans are still prone to make mistakes every time they use one. Normally, humans will take about 180–200 milliseconds to detect and respond to visual stimulus.[2] However, in most situations where a stopwatch is used, there are indicators that the timing event is about to happen, and the manual action of starting/stopping the timer can be much more accurate. The average measurement error using manual timing was evaluated to be around -0.04 s when compared to electronic timing, in this case for a running sprint.[3] To get more accurate results, most researchers use the propagation of uncertainty equation in order to reduce any error in experiments.[4] Well used ${\displaystyle \sigma _{Q}={\sqrt {\sigma _{a}^{2}+\sigma _{b}^{2}}}}$

• ${\displaystyle \sigma _{Q}}$is the sum of the uncertainty between ${\displaystyle \sigma _{a}^{2}}$ and ${\displaystyle \sigma _{b}^{2}}$
• ${\displaystyle \sigma _{a}}$ is the value which is actually found from the experiment.
• ${\displaystyle \sigma _{b}}$ is the value of the uncertainty.

For example: If the result from measuring the width of a window is 1.50 ± 0.05 m, 1.50 will be ${\displaystyle \sigma _{a}}$ and 0.05 will be ${\displaystyle \sigma _{b}}$.

## Unit

In most science experiments, researchers will normally use SI or the International System of Units on any of their experiments. For stopwatches, the units of time that are generally used when observing a stopwatch are minutes, seconds, and 'one-hundredth of a second'.[5]

## References

1. ^ "The History of the Digital Watch". h2g. Retrieved 28 Oct 2017.
2. ^ Jain, Aditya; Bansal, Ramta; Kumar, Avnish; Singh, KD (1991). "A comparative study of visual and auditory reaction times on the basis of gender and physical activity levels of medical first-year students". International Journal of Applied and Basic Medical Research. 5 (2): 124–7. doi:10.4103/2229-516X.157168. PMC 4456887. PMID 26097821.
3. ^
4. ^ "A Summary of Error Propagation" (PDF). a collage. Retrieved 10 October 2017.
5. ^ Gust, Jeff C.; Graham, Robert M.; Lombardi, Michael A. (January 2009). "Stopwatch and Timer Calibrations (2009 edition)" (PDF). Retrieved 10 October 2017. {{cite journal}}: Cite journal requires |journal= (help)

## Media files used on this page

Wooden hourglass 3.jpg
Author/Creator: User:S Sepp, Licence: CC-BY-SA-3.0
Alternative version of image:Wooden hourglass 2.jpg. Wooden hourglass. Total height:25 cm. Wooden disk diameter: 11.5 cm. Running time of the hourglass: 1 hour. Hourglass in other languages: 'timglas' (Swedishrtrttttyo), 'sanduhr' (German), 'sablier' (French), 'reloj de arena' (Spanish), 'zandloper' (Dutch), 'klepsydra' (Polish), 'přesýpací hodiny' (Czech), 'ampulheta' (Portuguese).
WPtimetracer.png
Author/Creator: unknown, Licence: CC BY 2.5
WP:Timeline Tracer logo
Omega Speedmaster Schumacher Edition10 36 22 158000.jpeg
Author/Creator: Pittigrilli~commonswiki, Licence: CC BY-SA 4.0
Omega Speedmaster Racing, Michael Schumacher Edition, 3518.50, Limitierte Auflage, Automatic
Stopwatch mode in cell phone.png
Author/Creator: Kunananya, Licence: CC BY-SA 4.0
Stopwatch mode in cell phone.
Schlagzahluhr stroke-timer ST-X3.jpg
Author/Creator: schlagzahluhren.de, Licence: CC BY-SA 3.0
Picture of ST-X3 stroke-timer by http://www.schlagzahluhren.de
Stopwatch.gif
Author/Creator: Lookang, Licence: CC BY-SA 3.0
A stopwatch is a hand-held timepiece designed to measure the amount of time elapsed from a particular time when activated to when the piece is deactivated.
Stopwatch, 1810201155, ako.jpg
(c) Ansgar Koreng / CC BY-SA 4.0
Focus stack of a vintage stopwatch. Focus stack of 25 pictures with Helicon Focus.
Louis Moinet's "Compteur de Tierces".jpg
Author/Creator: LouisMoinet, Licence: CC BY-SA 3.0
The first ever chronograph, although its maker, Louis Moinet, called it a “compteur de tierces.” According to hallmarks on the dust cover, the chronograph was started in 1815 and completed the following year.
Stopwatch in casio.jpg
Author/Creator: Kunananya, Licence: CC BY-SA 4.0
This is a stopwatch mode function in wristwatch.