Trumpf Tube
You should remember that there are no perfect tubes. They have bows. They may protrude from the interior as well as the exterior of the tube. It is difficult to process this material in a consistent and rapid manner when there are such inconsistencies among products.
What can you do to compensate? You will traditionally touch your face with a sensor to mark the contact point. The tube is then turned and touched on the other side. This gives the control an indication of how bent the tube is. This is a reliable method that can guarantee the through-holes are working for the application. However, this method reduces the ability to deliver extremely high tolerances for each rotation of the tube.