ElumTools provides a method to calculate only entities that you have selected beforehand in Revit. This command does not work with elements selected using "Tab-select" from linked models.
Using the Calculate Selected Elements command from the Calculate pull down menu, users can select any subset of the Revit model to establish the surface geometry to be considered in the calculation.
Caveat: Users should be aware that selecting an element will include all surfaces associated with that element, which may be more than what is desired. An example of this is including a floor element that happens to cover an entire level. Following this same logic, calculation points placed on Planar Faces, such as the floor example, will also cover the entire surface.
As an example of a practical use of the Calculate Selected Elements command, consider scalloping patterns from a downlight on a single wall. When considering luminaires for the project you may be interested in isolating only a single typical wall to evaluate the light patterns of different products together with spacing and setback. The following steps illustrate how this can be achieved very quickly.