A multiple exposure of the sun over the course of an entire day. First, I metered the correct exposure for a single image: 1/60 sec. @ f/22. Then I thought about how often I wanted to have the sun in the picture. The picture was to begin at 11:10 and end at 20:40, and I wanted to take an image every 30 minutes, so 20 images in total, all on one piece of film.
So, 20 images had to add up to 1/60 second at f/22. 1/60 divided by 20 resulted in an exposure of 1/1200 second at f/22 per image. Since I don't have a 1/1200 setting, I exposed 1/1500 second. That meant I was 1/300 sec. off at the end. 1/300 sec. is 1/5 of the required 1/60 sec.
Since the exposure on slide film needs to be very exact, I exposed (after metering the new correct exposure and dividing by 5) 1/750 sec. at f/5.6 in the early evening twilight.