QDC-501B (A) Alternating Pressure Mattress is made up by 18 pcs of 11cm/4.3'' cells. The Alternating System includes A/B/C 3 groups of cells design (6 cells per group). During alternating, there always have 2 groups of cells keep inflating, it means that it will have 12 cells can share and support the patient's weight. Compared with the A/B 2 groups alternating model(B) (just have 9 cells keep inflating at the same time), the share weight of the A/B/C Cycle Mode alternating mattress will be more average. The patient can feel more comfortable and have better sleeping quality.