Pressure switch two sets of relay output and a single relay output What is the difference between it

What do I think of the difference between the two? Or how the control method is different Please explain the popular point, thank you all

Double relay output is the lower limit of the pressure and the upper limit of a relay were issued, that is, you can adjust and set the lower pressure and upper limit.

Double relay output is the lower limit of the pressure and the upper limit of a relay were issued, that is, you can adjust and set the lower pressure and upper limit.

Single relay output is only in the lower limit of the set pressure or the upper limit of the output, that can only choose one.