Resource assignments, work, and assignment units and calendars all can affect the way Microsoft Project schedules.

Resource assignments

If you don't assign resources to tasks in your project, Microsoft Project calculates the schedule using task duration, task dependency, constraint, and project and task calendar information. If you do assign resources, the tasks are also scheduled according to resources' calendars and assignment units, providing for more accurate scheduling.

An assignment is the association of a specific task with a specific resource responsible for completing the task. More than one resource can be assigned to a task. Both work resources and material resources can be assigned to tasks.

For example, in your project you have a task named "Develop specifications." You also have an engineering resource, "Sean." If you assign Sean to the "Develop specifications" task, this intersection of the task and resource is the assignment. The scheduling of this task depends on Sean's resource calendar and assignment units, in addition to task information such as duration, dependencies, constraints, and calendars.

In addition to scheduling according to task information, after you assign resources to the tasks in your project, Microsoft Project has resource and assignment information to use in calculating, including:

• Work distribution over time   The amount of work or overtime work the resource is assigned to do, and how that work is distributed over time. This can also be affected by work contours.
• Number of resource assignment units   This number indicates whether resources are assigned on a task part time, full time, or multiple.
• Task types   Task types affect how a schedule changes if you revise the existing assignment. The three task types are fixed unit, fixed duration, and fixed work.
• Effort-driven scheduling   If a task is effort-driven, as resources are added or removed on the assignment, the work remains constant for the task and is redistributed among the resources. For fixed-unit tasks, for example, if more resources are assigned, it may take less time to complete the task.
• Resource calendars   Microsoft Project schedules assigned resources based on working and nonworking times, indicated on their resource calendars.

Unlike work resources, assigning material resources to a task does not affect task scheduling. However, editing material assignments can affect task scheduling if only material resources (and not work resources) are assigned to a task. In this case, changing the work of a variable material assignment can change the task duration. For example, suppose you have a material resource with assignment units of ten tons/hour, and the duration is eight hours. If you change the units to 20 tons/hour, the task duration will change to 16 hours.

Work

Work is the labor, time (in terms of minutes, hours, days, or weeks for work resources), or quantity (for material resources) required to complete a task or assignment.

Work is different from task duration. For example, a resource may require 32 hours of work to complete a task, but the task may be scheduled with a duration of two days. In this case, more than one resource needs to be assigned to this task. Working eight hours a day on the task, two people would complete the task in two days.

As soon as you assign a work resource to a task, work is calculated for the assignment. The way work is calculated depends on whether the task is effort-driven. For example, if you have an effort-driven task with a four-day duration, and you assign two resources to it, each resource is assigned to 16 hours of work. On the other hand, if you have a non-effort-driven task with a four-day duration, and you assign two resources to it, both resources are assigned to 32 hours of work.

Work can be viewed as timephased data in the Task Usage and Resource Usage view. In the timesheet portion of these views, the work is shown spread across the time period. You can contour this work in different shapes, such as a front-loaded, back-loaded, or bell shape.

You can also edit the work amounts for each time period yourself by manually tuning the work amounts in the timesheet portion of the Task Usage or Resource Usage view. However, be careful to account for the total work value across the assignment span. It's easy to add or remove work when making manual adjustments in a usage view, in which case you would be inadvertently changing the total work value shown in the Work field in the table portion of the usage view.

Assignment units and calendars

There are two types of units in Microsoft Project: maximum units and assignment units. When you want to specify how much a work resource is available for work on a project, you specify maximum units in the Resource Information dialog box or in a resource sheet. When you want to specify how much either a work resource or material resource is dedicated to a specific assignment, you specify assignment units. These unit types have different uses for work resources than they do for material resources.

To indicate the level of effort for a work resource on a specific assignment, you can enter the information in the Units field in the Resource Assignment dialog box or on the Resources tab of the Task Information dialog box.

Assignment units indicate how much of the resource's working time is being used for a particular task. For example, you can specify:

• 100%   If the resource is to work full-time on the assignment, based on the resource's working times calendar. This is the default for all assignments.
• 50%   If the resource is spending half of their time on this assignment. Even if the resource is a full-time resource, some assignments might only require a part-time effort, leaving the remaining time available for another assignment.
• 200%   If two full-time, equivalent, multiple resources are working on this assignment.
• 250%   If there are two full-time resources and one half-time resource on this assignment.

For material resources, the Units (or Assignment Units) field indicates the material consumption rate, that is, the number or rate of units of material being used for the assignment. There are two types of material assignment units: fixed and variable. Variable assignment units can affect the schedule.

A variable material consumption indicates that, as the task duration changes, the quantity of materials used changes proportionally. Likewise, if only variable material resources are assigned to a task, and if you change quantity, the task duration can change accordingly. Variable consumption is indicated with a time label added to the material label in the Assignment Units field. While fixed consumption of steel might have an assignment units value in "tons," variable consumption might have an assignment units value as "tons/day" or "tons/d."

For work resources, task schedules can also expand or contract based on the working times calendars of assigned work resources. Use the project calendar in the Change Working Time dialog box to set the standard working and nonworking times and days for all resources in the project. Use a resource calendar to set exceptions to working times for individual resources, for example, for days off or vacations.

Resource calendars and assignment units interact to determine assignment scheduling. For example, if Betty's resource calendar is set for eight hours of working time on Thursdays, and if she's scheduled 100% on a task for Thursday, work on the task equals eight hours. However, if Betty's resource calendar is set for four hours on Friday, and if she's scheduled 100% on a task for Friday, work on the task equals four hours.