Don't know about the select. But the Classic has a weight chart ( on the side). Set the pressure with the black knob according to your vehicle weight. That can usually be found in your toads door jam.
Second, if you want the BB to apply brakes quicker you can adjust the sensitivity setting - more green lights mean more sensitive for braking - less for lighter braking. Use the black button for that. Ours is set a 4 lights. According to BB it only works at around 15 mph or more. I know when mine is braking as the part that plugs into the 12v accessory connection turns green until braking stops.