Complex sentence: Most national standards permit the use of "at least a Class 2 instrument" and for many measurements, there is little practical point in using a Class 1 unit; these are best employed for research and law enforcement.
Split into simpler sentences: Most national standards permit the use of "at least a Class 2 instrument". For many measurements, there is little practical point in using a Class 1 unit; these are best employed for research and law enforcement.