MS Project - Task types Fixed Unit/Duration/Work simplified

There are 3 Task types in MS Project regardless of its different versions. They are Fixed Unit,Fixed Duration and Fixed Work. 

Before discussing them lets discuss a basic formula : 

                                              Work = Duration * Units

Scenario 1: If 1 person is doing a task for 2 days, then Work as per the above formula is

                                 Work = 2 * 8 = 16 hours.

1 Unit 100% equals to 1 person doing 8 hours of work. 1 Unit 50% means 1 person doing 4 hours of work.

Work: The effort for the task

Duration: The time period the task is done

Units: The number of people doing the task

Task types:

Fixed Unit: 

When Unit is fixed, if you change Duration or Work the other will change. In Scenario 1, you change the Duration to 3 days, Work = 3*8 = 24 hours OR change the Work to 24 hours,

Duration = 24/8 = 3 days.

Fixed here doesn't mean fixed once and for all. You may change the unit.

You may set a Fixed Unit task as either Effort driven or Non Effort driven. Effort driven means fixing the Work also.

In Scenario 1, with Effort driven,

If you change the units to 2 (which means 2*8=16 hours ), the duration will be changed to 1 day. Duration = Work / Unit= 16/16)

In Scenario 1, with Non Effort driven,

If you change the units to 2 (which means 2*8=16 hours ), the Work will be changed to 32.  

Fixed Duration:

When Duration is fixed, if you change Unit or Work the other will change. In Scenario 1, you change the Work to 24 hours, Work = 3*8 = 24 hours OR change the Work to 24 hours,

Duration = 24/8 = 3 days.

In Scenario 1, with Effort driven,

If you change the units to 2 , the Unit will be changed to 50% to maintain the Work at 16 hours. 16=2*8. 2 Units at 50% means 4 hours of work by one resource.For 2 Units 4+$=8.

In Scenario 1, with Non Effort driven,

If you change the units to 2 (which means 2*8=16 hours ), the Work will be changed to 32.  

Fixed Work:

Fixed Work is basically Effort driven.

In Scenario 1, if you add more resources, the duration will be reduced i.e. Work will not be changed.

How to change Task type: Double click on the task to see the Task information. Change the Task Type.

Default Task type is Fixed Unit, Non Effort driven.