What are the basic principles of differential pressure?

These are differential pressure sensors that will monitor the pressures in 2 spaces and let you know the differential between them.   

The HIGH port always gets plumbed to the area you care most about, and the LOW or REFERENCE port is always plumbed to the space you want to compare to.  

With our LITE, there is only one port that needs to be “plumbed” the other is integrated into the face of the unit (the little dots in the bottom left of the face).