Assigning Pay scale to Positions

Dear Experts;

There is a request to assign the pay scale to the position, that can help them know how many levels or grades have vacancies.

The case is, they have employees assigned to positions with a specific grade, then they are transferred from unit to another without having changes in their grades so their previous positions have been vacant but their grades are not as they are still on the same grade.

While another case if the employee got promoted to another grade then his previous one has been vacant.

How can this be done?

Thanks in advance.

Best Regards;

Lobna