A stopwatch is a mechanism designed to measure the interval of time between the moment we start it till the moment we stop it. It's mostly used to measure time for a distance, we can see it in sports like swimming, marathoons, athletics and for motorsports like Formula 1.
There is two kind of stopwatch in term of manuel/automatic. The manual have two buttons, a person presses the one in the top to start the timmer, and pressing it for second time stopsit or mark a period of time elapsed between start-stop, however the button in the bottom resets the timer, pressing the split button for a second time resume or restart the stopwatch. An automatic stopwatch uses sensors to trigger a start and stop events.
We can also classify stopwatch into mechanical and digital, the design of the mechanical one is based on a mainspring, which is is a spiral torsion spring of metal ribbon, which can be worn quickly, that reduces the accuracy of the stopwatch.
In the other side, the design of the digital is based on a crystal oscillator timing element, it's much more accurate than the mechanical one.
There are a lot of stopwatch avalaible as websites, or android apps, or included as operating system mini tool, there is even libraries in java that permit to you to calculate the amount of time the execution of a function takes, you just have to create a new instance before calling the function and after the business is done, and don't forget to log the timer instace into the console.
Finally, I would like to say that we are giving our best to provide the most complete stopwatch possible, we are trying to provide a tool with sweet design and cool functionnalties and as accurate as possible.