If I were going to be using "guesstimates" by anyone as to what pressure I should be using, I'd want the machine to be an autopap (auto-titrating cpap) set for a range of pressure, not just a machine delivering a single pressure that I was supposed to move up based on how I felt. Ideally, an autopap will sense from your breathing how much pressure is needed and adjust up and down automatically throughout the night.
A full PSG sleep study would be best, of course, but if you really have to settle for the kind of test they gave you, do push for an autopap. I personally would also want to get the software to download and look at the data myself on my own computer each morning. But the software is usually something you have to get for yourself...doesn't come with a machine. Software can be purchased from online cpap supply stores without a prescription.
I'd also want the sleep doctor or "person" in charge of my case to order a couple of nights with a recording pulse oximeter while I'm using the cpap or autopap at home to see if the treatment is, indeed, keeping my oxygen levels up well all night.
If you have to
go this route without a full sleep study and a prescribed pressure I'd consider an autopap and the software for it to be essential tools. Heck, even after a full sleep study and formally prescribed pressure, I still think it's a good idea to at least have a trial using an autopap that can yield further info over a period of time about how much pressure the machine has to use throughout the night when you're sleeping in your own environment and in your usual sleep positions.
Good luck Maggie and Debbie. They're asking you to manage figuring out a lot of things on your own. It's doable, but only if you educate yourself as much as possible via the message boards...this board and the boards at talkaboutsleep.com and cpaptalk.com. You can do it, but do keep digging into the message boards as if you were a med student studying for the exam of your life.