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. 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. To get more accurate results, most researchers use the propagation of uncertainty equation in order to reduce any error in experiments. Well used is the sum of the uncertainty between and is the value which is actually found from the experiment. 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 and 0.05 will be . 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'. Types of stopwatches See also Chronograph Samuel Watson (horologist), maker of the first stopwatch Time clock Timekeeper Time to digital converter Timer The Stopwatch Gang References External links Open Source Physics Stop Watch Computer Model NIST Recommended Practice Guide: Special Publication 960-12 Stopwatch and Timer Calibrations Timers Portable tools