1. // =================================================================
2. //global variables / objects
   
3. StopWatchTimer sw;
4. // =================================================================
5. // Main functions
6. void setup() {
7.   size(400, 400);
8.   sw = new StopWatchTimer();
9.   sw.start();
10. }
11. void draw () {
12.   time();
13. }
14. // =================================================================
15. // Other functions
16. void time() {
17.   background(#FFFFFF);
18.   fill(#000000);
19.   textAlign(CENTER);
20.   // textFont(words, 50);
21.   text(second(), 350, 175);
22.   text(":", 300, 175);
23.   text(minute(), 250, 175);
24.   text(":", 200, 175);
25.   text(hour(), 150, 175);
26. }
27. // =================================================
28. // classes
29. class StopWatchTimer {
30.   int startTime = 0, stopTime = 0;
31.   boolean running = false; 
32.   void start() {
33.     startTime = millis();
34.     running = true;
35.   }
36.   void stop() {
37.     stopTime = millis();
38.     running = false;
39.   }
40.   int getElapsedTime() {
41.     int elapsed;
42.     if (running) {
43.       elapsed = (millis() - startTime);
44.     }
45.     else {
46.       elapsed = (stopTime - startTime);
47.     }
48.     return elapsed;
49.   }
50.   int second() {
51.     return (getElapsedTime() / 1000) % 60;
52.   }
53.   int minute() {
54.     return (getElapsedTime() / (1000*60)) % 60;
55.   }
56.   int hour() {
57.     return (getElapsedTime() / (1000*60*60)) % 24;
58.   }
59. }
60. // ====================================================

well, thanks to the other guys, jbum and phi.lho, I really only put the pieces together... and that also wrong... 

text(nf(sw.hour(), 2)+":"+nf(sw.minute(), 2)+":"+nf(sw.second(), 2), 150, 175);

change to:

 text(nf(sw.hour(), 2)+":"+nf(sw.minute(), 2)+":"+nf(sw.second(), 2)+":"+nf(sw.hundrensec(), 2), 150, 175);

1. void mousePressed()
   
2. {
   
3.   if (mouseButton==LEFT)
   
4.   {
   
5.    sw.stop();
   
6.   }
   
7.   else if (mouseButton==RIGHT)
   
8.  {
   
9.    sw.start();
   
10.  }
    
11.  
    
12. }
13.  
14. // And add in the class  before  int second() this :
16.  int hundrensec()
    
17.   {
     
18.   return (getElapsedTime() / 10) % 100;
    
19.   }