String dataDir = Utils.getDataDir(AssignmentCost.class);
        
Project project = new Project(dataDir + "New project 2013.mpp");

Task task = project.getRootTask().getChildren().add("t1");

Resource materialResource = project.getResources().add("materialResource");
materialResource.set(Rsc.TYPE, ResourceType.Material);

Resource nonMaterialResource = project.getResources().add("nonMaterialResource");
nonMaterialResource.set(Rsc.TYPE, ResourceType.Work);

ResourceAssignment materialResourceAssignment = project.getResourceAssignments().add(task, materialResource);
materialResourceAssignment.set(Asn.RATE_SCALE, RateScaleType.Week);

ResourceAssignment nonMaterialResourceAssignment = project.getResourceAssignments().add(task, nonMaterialResource);
nonMaterialResourceAssignment.set(Asn.RATE_SCALE, RateScaleType.Week);

project.save("output.mpp", SaveFileFormat.MPP);

Project resavedProject = new Project("output.mpp");

ResourceAssignment resavedMaterialResourceAssignment = resavedProject.getResourceAssignments().getByUid(1);
System.out.println(resavedMaterialResourceAssignment.get(Asn.RATE_SCALE));

// only material resource assignments can have non-zero rate scale value.
ResourceAssignment resavedNonMaterialResourceAssignment = resavedProject.getResourceAssignments().getByUid(2);