How is a ranger finder/laser level a laser pointer ? Why is that allowed, but competitors cannot use a tape measure to measure from launch to center of target. Ranger finders so the exact same thing.

General rule #1 applies here. The rules do not prohibit any kind of measuring devices so they are therefore allowed. Rule 3.f. does prohibit the use of electronic components in the device and trigger but allows them for sighting as long as they are removed before the launch. The laser pointer is one example and not an exclusive type of device allowed.