I am reading manuals and searching the web for two hours but can't find a solution to my problem:

I have a task with a fixed "work" of 20 hours and a duration of 10 days (on average 2 hours a day). Now I want to allocate two resources (employees) to this task and I want MS project to set the unites of these two resources automatically. In this example this would mean that each employee works 1 hour a day on the project (12.5%). But I can't find a way to to this. Also, in case I would change "work" or "duration" I would want the resources/units to be changed automatically too (e.g. if I change work to 40 hours, but duration remains the same, the two employees would have to work 25% of their time on the task).

Any help is highly appreciated!
Joe