Suunto D4 User Manual page 54

The depth of the ceiling and floor will depend on your dive profile. The ceiling depth
will be fairly shallow when you enter the decompression mode, but if you remain at
depth, it will move downward and the ascent time will increase. Likewise, the floor and
ceiling may change upwards while you are decompressing.
When conditions are rough, it may be difficult to maintain a constant depth near the
surface. In such cases, it is more manageable to maintain an additional distance below
the ceiling, to make sure that the waves do not lift you above the ceiling. Suunto re-
commends that decompression takes place deeper than 4 m/13 ft, even if the indicated
ceiling is shallower.
NOTE
WARNING
It will take more time and more air to decompress below the ceiling
than at the ceiling.
NEVER ASCEND ABOVE THE CEILING! You must not ascend
above the ceiling during your decompression. In order to avoid
doing so by accident, you should stay somewhat below the ceiling.
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