The standard Poseidon MKVI is a recreational non-decompression dive rebreather with a max depth of 40 meters.
This means that the unit will guide the diver to stay above 40 meters and not get into a decompression dive.
Should the diver go deeper than 40 meters and/or go in to a deco dive, the unit will alert the diver by using light, sound and vibration alarm signals and it will also support the diver all the way to the surface, even if it requires decompression stops. It will also work at depth greater than 40 meters but it's not recommended.
If you want to dive deeper or with decompression stops you have the following options:
40M Deco Battery - Allows you to dive to 40M with decompression stops.
48M Deco Trimix Battery - Allows you to dive to 48M with decompression stops and trimix in the diliuent.
60; Hardware/Firmware Upgrade - Allows you to dive to 60M with decompression stops and trimix in the diluent.