Otherwise, just set it for 15 cm and see if it works for you. A fixed CPAP is still about 95% as medically effective as an APAP, generally speaking. But you want APAP if you can swing it.
Newer machines are also data-capable, which is helpful. We can get you up to speed on that.
1982 is pretty early. I wish I had started then. But you were a pioneer; in 1985 there were only ~100 SA patients using CPAP at home in the US.