public function start() : Stopwatch
    {
        Preconditions::checkState(!$this->isRunning, 'This stopwatch is already running.');
        $this->isRunning = true;
        $this->startTick = $this->ticker->read();
        return $this;
    }
public function start() : Stopwatch
    {
        Preconditions::checkState(!$this->isRunning, 'This stopwatch is already running.');
        $this->isRunning = true;
        $this->startTick = $this->ticker->read();
        return $this;
    }
public function start ( ) : Stopwatch { Preconditions :: checkState ( ! $ this -> isRunning , 'This stopwatch is already running.' ) ; $ this -> isRunning = true ; $ this -> startTick = $ this -> ticker -> read ( ) ; return $ this ; }
Starts the stopwatch.

@return $this
@throws IllegalStateException if this Stopwatch is already running
Starts the stopwatch .