What you see is what you get:

The SX-4150 ROLLCHECK® MINI is a compact and easy to use laser alignment tool system. This product is extremely lightweight, and attaches to rolls up to 4 inches in diameter.

Because we understand how important it is to receive an accurate reading, the ROLLCHECK® MINI uses cutting-edge laser beam technology. This system works by projecting a laser on to a reflector, which you mount on the roll you are aligning.

After reflecting from the roll back to the reference line, instantly see whether your rolls are parallel. There is nothing more important to us than simplicity. This is why the SX-4150 ROLLCHECK® MINI, like all of our laser roll alignment tools, is easy to use with no training required. A single person can check roll alignment with this device in less than a minute.