The second is the standard unit used to measure time intervals. Multiple seconds can accumulate to make up minutes, hours and days. Sometimes seconds are divided into smaller intervals or fractions of seconds like milliseconds and microseconds. The smallest time interval the device is capable of measuring is the resolution.

The traditional analog stopwatch uses a spring mechanism to move a needle in a circle along a calibrated dial. The needle movement starts and stops when the user activates and deactivates the device by pushing a button. Winding the watch occasionally keeps the spring tight and ensures reliable performance.

An electronic stopwatch measures time using a crystal oscillator. It records the vibrations of crystals. Quartz crystal is most often used in a timing device. This type of watch displays the time interval measured in numeric form on a liquid-crystal display screen. An electronic model is more accurate than a manual stopwatch when measuring intervals less than a second.

Sophisticated models feature a variety of functions and are some equipped with multiple displays for tracking several events simultaneously. Some have enough memory to record hundreds of events and makes them accessible to the user for review. They are useful for timing multiple laps and will display the fastest lap, the slowest lap and an average lap time. It is also possible to record the time of day an event started and ended.

A countdown stopwatch counts down to zero from any preset time. A repeating countdown timer will count to zero from a preset time and automatically begin a new countdown from the same preset time. Some of these models have multiple timers that work independently. Models with linked timers will automatically start a new countdown after the previous timer reaches zero.

Stopwatches are most often associated with sports because they are used to time athletes during training sessions. Motor sports of all kinds use timers to calculate how fast a vehicle is moving or measure the precise interval between two vehicles on the track. In the entertainment industry, filmmakers use them to time scenes. Prices vary widely depending on functionality but consumers can find products to suit any need and budget.