What is a stopwatch?
A stopwatch is a special type of timepiece. It is a handheld watch that is made to time events. It has buttons to start and stop timing an event and will show the amount of time that has elapsed from when it was started to the stop time.
There are many things about a stopwatch that you can measure. You might want to know the mass, weight, diameter, thickness, temperature, conductivity, or cost of the stopwatch, and they all have different units. Of course, the stopwatch itself measures time, and the unit of THAT is the second, in both SI and US Customary units.
The primary use of a stopwatch is to time the duration of an event. Example: how many minutes/seconds does it take for a runner to race one mile -- "start" the stopwatch when the starting gun fires, then click "stop" as the runner crosses the finish line. You can try a stopwatch yourself on-line to get a sense of how it works and give you ideas of what you might be able to use it…