Is the only difference between an Auto bilevel and an auto cpap (besides price) that the auto biIlevel can be set at 2 pressures and has a maximum of 25 cmwp while the auto cpap only goes to 20 cmwp? The S9 reduces the exhale pressure by 1-3 cmwp and the REMStar by 1-3 somethings. How much does the REMStar actually reduce the exhale pressure? Does this reduction in exhale pressure work in the auto mode in both machines? Which machine gives the best (most complete) data? Overall which machine do you think is the best? My doctor did not ask to see me after writing a prescription. He wrote Auto pap 5-20 cm's of pressure. I think he meant an Auto cpap. He also wrote RAMP 30- 45. Although I know what ramp means in general, not sure what he meant here. Ramp to 5 cmwp ???