Inside the instrument, there is a sealed aneroid barometer.
From the en.wikipedia.org
The technology is licensed to Canberra Albuquerque, which has helped transform LBIMS from a demonstration system into a fully packaged instrument housed in a robust security-sealed enclosure.
From the sciencedaily.com
If it is suspected that the problem is condensation, then a room should be sealed off with a dehumidifier left running for the recommended time and then further instrument tests made.