Units % not updating when multiple resources assigned

David, You're right, it can seem a little strange. And in fact the definition of Assignment Units was changed with the introduction of Project 2010. The field you want to see is the Peak field. That field will show what you are expecting to see (i.e. 50% for the first resource and then 25% when the second resource is added). I suggest you check the Project help file for the Peak field (hover your mouse over the Peak field heading and then hit F1). When the help window pops up, enter Peak. The help file gives some insight as to why the change was made.

An interesting observation is this. Add a third resource. You will see the Peak field show 17% while the Assignment Units field still shows 50% for the first two resources but 25% for the added resource. As you add more resources, the Assignment Units field will "lag" the units value.

Hope this helps.

John