Well, this will depend on the task that you try to execute. What's important is meeting the level of accuracy that is needed for the job. You’ll find that old laser levels have a tolerance rating that can go from 1 to 8 millimeters in 20 meters. Anything within that given range can be used for interior jobs of short distances. On the other hand, for exterior jobs that go long distances, having a laser that goes from 1 millimeter to 4 millimeters in 20 meters will do the trick. But when it comes to a highly specialized engineering job, the tolerance rating becomes essential.