They are divided into three categories: Those who inspect the locomotive and cars, those who inspect the operations, and those who inspect the engineering and the infrastructure.
An inspector generally starts with a visual inspection. If it is okay, fine. However, if the inspector wants to dig a little deeper, he will go into the office. He will then look at documents, at the training program and at anything else which falls under his mandate. For example, he might look into when an employee was trained and then review the training program. He will also examine whether the employee is doing a good job or not. He will look at supervision. He will review all the methods and policies which are in place to support what he saw on the ground.
So inspectors have to do these two things in the course of their work.