Instructions: Lets say you're using an exposure of 5 seconds and an interval between the exposures of 10. Your total interval is therefore 15 seconds. Lets also assume that you want your shot to be 20 seconds long - thats 500 frames. (25 frames per second - assuming pal video transfer - multiplied by 20 seconds).

Look at the 1 to 20 second graph. Read up from the bottom until you hit the orange (500 frame) line and then read across to the number of minutes - for a 15 second interval your shot will take you 125 minutes.