Pressing the "Start" button
    turns on a relay for a fixed duration (set by the potentiometer).  
Timing operation
    can be manually terminated at any time by pressing the "Reset"
    button. 
Slide switch (S1) sets the range :   from 0.5 sec. to 50
    sec.  -or-   from 1 sec. to 100 sec.
    
    Applications :  
General purpose timer, pvc bags
    sealing machine timer, game timer, ...