Precedence Diagramming Method. We start from 0 or from 1?

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01:00 – Drawing the precedence diagram using the PDM (AON) method
02:15 – Calculation starting from 0
09:30 – Linking the two calculation time scales
10:40 – Calculation starting from 1
15:20 – Conclusions

Before you start, I want to tell you that I made 2 mistakes in the presentation. Can you find them?

In this second video of our series, we will look deeper into the precedence diagramming method and discover two different calculation methods.

I noticed that people may be confused when they do the calculations of the start and finish times of the activities and they see two different calculation methods.
The first calculation method starts from the point or even 0 and uses a continuous time scale. The calculations are very simple and provide in some cases comfort to the people doing the calculations.
On the other hand, the second way of calculation, and the one that is today mostly used (also in the software) starts from 1 and counts the period, like days. This method is more natural because we do not have a day 0, a week 0, month 0 and finally year 0.
The calculation method uses ordinal number to determine the start and finish of activities. For example a working day start typically at 08:00 or 09:00 to finish at 17:00 or 18:00. An activity with a duration of 1 day will start at day at 08:00 and finish at 17:00. The next activity will then start on day 2 at 08:00 and so on.

These different methods may be a bit confusing for some people but are completely equivalent, however, we will identify some differences between them.

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