Know the Basic Scheduling Formula

Duration = Work/Units

Understanding  of  the  meaning  of  these  three  terms (See Project Help), as well as the formula itself, is key to  understanding  how  Project  schedules  a  task.    To anyone who has changed any of these three parameters on  a  task,  without  understanding  this  formula,  the  changes  that  Project  makes  to  the  other  parameter(s) can sometimes seem totally unexpected or bizarre.

Not  knowing  this  formula  is  the  biggest  cause  of  frustration  that  people  experience with  the  tool.  Knowing  the  formula  will  not  stop  Project  from  doing  things  that  you  don’t  expect,  but  it  will allow you to know what changes to make so that it will do what you want.

Use Task Types correctly

What  will  Project  do  when  you  change  either  work,  duration or units on a task – that is, which of the others will  it  change  and  which  will  it  keep  constant?      The  Task  Type  parameter  is  what  tells  Project  how  to  behave.  The general rule is:

If  work,  units  or  duration  is  fixed  and  you change one of the others, Project will recalculate the third, but wont change the one that’s “fixed”.

Even  if  you  don’t  set  task  type  explicitly,  each  task  defaults to one of the three – and the system default is “Fixed  Units”.    This  can  cause  problems  in  many cases, because since most technical tasks are driven by the   amount   of   work   effort   required,   they   should generally be “fixed work”

Understand the Effort Driven Task setting

If  a  task  is  effort  driven,  the  total  task  work  will remain  the  same  if  you  add  or  remove  resources.  If you  add  a  resource,  the  total  amount  of  work  effort  will  be  divided  among  all  of  the  resources,  including  the new ones, thereby reducing duration.

Good practice when adding resources to a task, even if  you  do  understand  this  concept,  is  to explicitly specify the work and units for each assignment, so you remain in control of the division of labour.  Do this in a usage view or the bottom half of a split-screen view.