A shutter as we learned is nothing but a door that lets light into the light tight box called camera. The door is on a timer like a bank fault. The timer tells the door how long to stay open. The time lock is in fractions of a second... the numbers on the dial are the demoninators again so 1000 is 1/1000 of a second ect... Now you understand the two man functions of the camera next I'll explain how they interact. Even if you dont want me to I will anyway.