The 2456-LEM ambient conditions monitor can be setup in COMPASS for Pressure as an Autodetect device (easy and recommended) or a non-Autodetect device (more difficult).
See the pdf document below named "2456-LEM COMPASS Autodetect Setup.pdf"
Here's the important screen-shot from COMPASS for Pressure. The RS232 communications need to be 9600, N, 8, 1 (see the document).
See the pdf document below named "2456-LEM communication with COMPASS, non-Autodetect.pdf"
For troubleshooting it's a good idea to troubleshoot a 2456-LEM with LEMcal software before troubleshooting with COMPASS for Pressure. See the Article at this link, LEMcal troubleshooting
If you need more assistance or have questions please contact Pressure Technical Support at the link below or call us at +1.877.355.3225