@CanIgnoreReturnValue
  public Stopwatch start() {
    checkState(!isRunning, "This stopwatch is already running.");
    isRunning = true;
    startTick = ticker.read();
    return this;
  }
@CanIgnoreReturnValue
  public Stopwatch start() {
    checkState(!isRunning, "This stopwatch is already running.");
    isRunning = true;
    startTick = ticker.read();
    return this;
  }
@ CanIgnoreReturnValue public Stopwatch start ( ) { checkState ( ! isRunning , "This stopwatch is already running." ) ; isRunning = true ; startTick = ticker . read ( ) ; return this ; }
Starts the stopwatch.

@return this {@code Stopwatch} instance
@throws IllegalStateException if the stopwatch is already running.
Starts the stopwatch .