Bests & Worsts Reviews from Amazon

My firm bought two of these to test the wall construction of a new medical clinic we designed; we wanted to verify that the wall construction was meeting its designed STC rating. When both meters are placed side by side pointing at the same noise source they generally read 15-30 dB different with no discernable consistency in relation to one another. While I understand these units are not the most accurate, and our testing method was not performed in a laboratory, you would think two units side by side would have a similar reading or be reading a consistent difference.