MS Project Tips and Tricks - Task Modes
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TLDR: Change the Task Mode settings in Microsoft Project so the default mode for all activities is Auto Scheduled (change in bottom left corner) and ensure all activities in the Task Mode column are set to same. Manually Scheduled mode is only appropriate for a high level summary schedule where critical path methodology is not required.
One of the most common issues I see is people not using the right settings in MS Project. Often people open project and then just start a new file with the default template that Microsoft provides in the program.
One of those defaults settings is the task mode setting. What does the task mode setting do? Well it determines whether the program will calculate new dates when logic is changed or added or when an activity duration is changed for example.
There are two options for Task Mode: Manual Scheduled and Auto Scheduled.
This can be set as a default for an entire schedule by changing the setting at the bottom left corner of your screen.
Change Task Mode setting for new tasks in the bottom left corner of program pane.
It can also be set for every activity in a schedule, and more importantly, there can be activities using both modes. For me as a practitioner that has been doing this for over 20 years I fall into the camp of using Critical Path Methodology in my schedules and therefore use the Auto Scheduled mode. If you're one who has also used scheduling software like Primavera P6, there is no such thing as a manual mode and there is certainly not an option to have a mixture of both.
Activity Task Mode setting for each activity. Manually scheduled are denoted by a thumbtack icon. Auto scheduled are denoted by a bar with an arrow.
Now why did Microsoft make this an option to choose from? There are situations where one just needs to create a high level indicative schedule or timeline of a project or something else. Without having to worry about calculating things like lags, logic, etc, in manual mode you can just quickly bang out a few activities, put some dates and durations to them and away you go for your presentation or whatever it is you're trying to show. This is a situation where critical path scheduling is not really applicable nor required. And manual mode for this makes sense.
However, in practice, I often see schedules where the schedule has a mix of both modes. And from a critical path methodology point of view, this is a problem for several reasons. First and foremost, if there are activities that are in auto scheduling mode and they have successor activities that are in manual mode, any changes to the activity in auto mode will change the dates of the activity in manual mode. Therefore this may give a false impression that a schedule may on track when in fact there are delays that are hidden in the schedule due to the use of a manually scheduled activities.
In the example below there are five activities, all with one day durations scheduled to occur sequentially. Note the mix of Auto and Manually scheduled mode. Now with the changes in duration representing some kind of delay, note how the Manual 3 activity dates so not change and therefore do not flow through to Auto 2. If the modes for all activities are set to Auto, the correct calculation is performed by the software.
I see no practical reason for mixing the modes. Even if applied to summary milestones. These should be set to auto mode and driven by the appropriate logic from an activity in the schedule any changes recalculates the correct dates. And the same issue does arise if milestones only have a constraint applied with no logic. But I would rather see that with the milestone in auto mode rather than in manual mode. However if was reviewing that schedule it would get flagged as missing logic.
Instead of going through this small change in setting when creating a new schedule file, create your own template with the mode already set to Auto mode.