When you create or edit a project, you have the choice of two different task scheduling project methods: Fixed work and Fixed duration.
When using the Fixed work scheduling method an additional column for Budgeted work is added and shown in the activity list:
Fixed work introduces both the Budgeted Work and the Earned value columns. This method focuses on budgeted hours rather than simply the duration of a task. This means that the duration of a task is automatically calculated by the budgeted hours and the amount of users put to this task. Note that the Earned value columns requires that the Earned value module is activated.
Example: You have budgeted 32 hours for a task (and use a standard 8 hour working day). Within this scenario, the task would then take one user 4 working days to perform. Alternatively, if we were to put two users on the task, it will take just 2 working days to perform. To take the example even further, having only one user working at a capacity of 50% on the task, it would take 8 working days to perform.
Fixed duration uses a simple yes/no condition to measure if the task is complete whereas the Fixed work method uses a percentage value to measure the degree of completion of a task. The actual work column automatically computes how many working hours have been added to the task, based on the percentage of completion of the task and the budgeted work.