when I change the resourse units in a task it changes the start o.

[MSP]

When I change the resource units in a task it changes the start or finish
dates and I don't want those dates modified.

 

[Jan De Messemaeker]

Hi,

It's probably not changing the start date but it changes duration and hence
finish.
To avoid that select the task(s), click the Task information button and on
the advanced tab select fixed duration as task type.
HTH

 

[Steve House [Project MVP]]

The length of time it takes to do most tasks is dependent on how hard the
resources doing the work, work. When you change the resource units you are
changing the rate at which the resources do the work - that's why they're
called "effort units." There are exceptions of course - a 1 hour meeting is
going to take 1 hour regardless of whether 2 or 5 people attend but for 99%
of the tasks in most real world projects, Project's normal behaviour
changing the task duration in response to changing resource units is an
accurate model of reality.