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The End of Day Convention

When we do CPM calculations in an academic way, we use something called the "End of Day Convention" to help make the math a bit easier to follow along. This video explains how that works.

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Now we want to talk about something that may not be very important as far as calculations. But it's very important when you go from the textbook to the computer software, and you will see something that's different. In the textbook approach in most textbooks, as far as I know, we always deal with the day as end of the day. Well, we had a choice to go from the beginning of the day or end of the day and we chose end of the day, perhaps because the most important date for any project is the end date.

And usually, end date means end-of-business date. When we say the project has to finish on the 30th of October, for example, it means end-of-business day. So end of the day is the most important thing. And when we start an activity, we start usually at the beginning of the day but only to be consistent. We use end of the day, we take the day before, so if the activity is starting on day 5, we say end of day 4, and if it's starting on day 10, we say end of day 9.

We can see one of those examples that we did. And we see that, for example, activity A starts on day 0, practically end of day 0 is the beginning of day 1. And in this case, if we subtract the finish date minus early date, it should be exactly equal to the duration. Activity A's duration is five days. So five minus zero is five. Go to activity J, for example, it's 15 and 17. So, 17 minus 15 is 2, or if yo...

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