Here is a guide to using the iPhone's Stopwatch and Timer.
The iPhone firmware's built-in clock function is highly comprehensive. The World Clock itself allows you to pick identifiable cities in all available time zones so that not only will you have your local time on your iPhone displayed, but you will also have a long list of other location times so that you can browse easily. This is perfect for the growing international communities where people may live in London, have their base job location in New York, and have family that lives in Busan, South Korea.
Along with this is an Alarm system that allows you to schedule a whole host of different "wake up" alerts in a way that stands independent. The clock's alarm is a nice addition because it does not have to be tied to a specific event, as it is in the iPhone's Calendar. This leaves two more important, but often looked over, clock functions. The Stopwatch and the Timer are also nice iPhone clock features that can have their own place in your normal iPhone usage.
The Timer, which you will find in the clock task bar at the far right side, is what you would expect by the name. The top view will be the "rolodex" appearance that allows you to set a specific amount of time you want the iPhone's Timer to go for. For example, you can set the Timer for one hour and seventeen minutes, and it will count down from there.
Directly below that will be the option to set the kind of sound you want for when the Timer finishes, which can range anywhere from normal alert sounds to iPhone ringtones. At the bottom of the Timer screen will be a green Start button.
The iPhone's Stopwatch can also be found in the clock, and you can select it from the lower task bar in between Alarm and Timer. The iPhone's Stopwatch is an even simpler interface than the Timer. There is a time listing at the top that shows hours, minutes and seconds. Below that are simple Start and Reset buttons. When you start the Stopwatch it begins counting up the time. Once you hit the Lap button, which shows up while the Stopwatch is counting, it will mark the time in that you hit the button in the list below. To the left is the Stop button you can hit, which will just freeze it. You can then hit Reset to bring it back to zero and erase all of the Lap times you had listed.