The General tab of the Resource Information dialog Project allows you to contour the Max Units for a resource over time. This means that you can specify a date range and the Max Units for that resource during that time period. This can be useful when you know that a specific resource will only be available to your project half-time for the month of June, but then full- time for July and August, and then half-time again in September.
Defining Constant Availability
Double-click on the resource you want to define.
To set the resource so that it has a constant Max Units over time, make sure that the Available From and Available To fields both read NA.
Make sure that the Units value equals the Max Units value you want to set for the resource.