A fixed pressure CPAP device provides a constant therapeutic pressure. The prescription is written as a single pressure such as 12 cmH2O.

An Auto adjusting CPAP provides a variable therapeutic pressure throughout the resting period. The prescription for it is written as a range of pressures such as 4-20 cmH20. The therapy will start at the lowest set pressure and then increase as it senses resistance.

The Z2 CPAP is no longer available in the US. Only the Z2 Auto is available for sale which can be set either in CPAP or APAP mode according to the prescription.