Product review (3 stars): Works as it should but.....
I'm using it for calibration of indoor thermostats. Assuming it is accurate, it works as it is supposed to. The meter and most thermostats vary from 2 - 4 degrees and from 4 - 6 percentage points on RH so it is helpful for calibration. The reason for 3 star rating is because all 4 screws connecting the front and back cover were missing. That quality control issue makes me question the rest of the device. I discovered this by accident. I was unscrewing the battery cover and had not quite got the screw out all of the way. I pulled on the battery cover and the rear cover came off. I wrapped some tape around it but disappointing for ~$200 device.

Thanks to those who mentioned the dust cap issue. I removed it very carefully and had no problem.