PROJECT 2010 MANUALLY SCHEDULED TASKS.
Microsoft Project 2010 introduced manually scheduled tasks. In prior versions of Project, all tasks were "automatically scheduled." The primary difference is the extent to which changes to one part of a project affect scheduling of tasks elsewhere --
Manual: You enter start and finish dates and regardless of other changes in the project the task remains scheduled for those dates unless you change them.
Automatic: You enter start date and estimated duration and Project schedules the task based upon that information together with any specified relationships and constraints. Scheduling of the task will automatically be updated to reflect changes elsewhere in the project
The default mode in Project 2010 is "manual." You can change the mode of an individual task to "automatic in the "task mode" field. You can change the default task mode to "automatic" by changing the program options for the specific project file. The Microsoft web site has a detailed discussion of the different task modes at "How scheduling works in Project."