Why does chronometer begin to count up when an Activity starts?

Question

When I launch the app with the widget Chronometer, this counts up itself parallel to the android activity when this is botted . I put a button for example and I added in the listener the method chronometer.start(). When I press the button, the time had already counted. It is like both Activity and Chronometer start parallel without any handle for the user. I was looking for solutions and I founded it how to implement and manage but I will know the reason why this happen. This is my code:

public class MainActivity extends AppCompatActivity {
Chronometer chronometer;
Button button_record;
Button button_stop;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    button_record = (Button)findViewById(R.id.button_record);
    button_stop = (Button)findViewById(R.id.button_stop);
    chronometer = (Chronometer)findViewById(R.id.chronometer_mic);

    button_record.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
                chronometer.start(); // Here the time was counted up when the app is booted or Activity 
        }
    });

    button_stop.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            chronometer.stop();
        }
    });
}

}