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Suunto EON Steel Black User Guide 3.0

Decompression dives

When on a decompression (deco) dive you exceed the no decompression limit, Suunto EON Steel Black provides the decompression information required for ascent. Ascent information is always presented with two values:

  • ceiling: depth that you should not go above
  • asc. time: optimum ascent time in minutes to surface with given gases

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.

On a decompression dive, there can be three kinds of stops:

  • Safety stop: this is a recommended three-minute stop for every dive over 10 meters (33 ft).
  • Deepstop: this is a recommended stop when you dive deeper than 20 m (66 ft).
  • Decompression stop: this is a compulsory stop on your decompression dive that is for your safety, preventing decompression sickness.

In Dive settings » Parameters, you can

  • turn deepstops on or off (it is on by default)
  • adjust the safety stop time to be 3, 4 or 5 minutes (default is 3 minutes)
  • set last stop depth to 3.0 m or 6.0 m (default is 3.0 m)

The following illustration shows a decompression dive where the ceiling is at 17.7 m (58 ft):

deco dive steel black

From bottom to top you see the following in the above image:

  1. There is a decompression window (Deco window) that is the distance between the decompression ceiling (Deco ceiling) plus 3.0 m (9.8 ft) and the decompression ceiling. So the decom window in this example is between 20.7 m (68 ft) and 17.7 m (58 ft). This is the area where decompression takes place. The closer to the ceiling you stay, the more optimal the decompression time is.

    When you ascend close to the ceiling depth and enter the deco window area, two arrows appear in front of the ceiling depth value. The downward and upward pointing white arrows indicate that you are within the deco window.

  2. If you ascend above the ceiling depth, there is still a safe margin area, equaling to ceiling depth minus 0.6 meters (2 ft). So in this example, it is between 17.7 m (58 ft) and 17.1 m (56 ft). In this safe margin area, decompression calculation still continues, but you are advised to go down below the ceiling depth. This is indicated by the ceiling depth number turning yellow with a downward pointing yellow arrow in front of it.

  3. If you go above the safe margin area, the decompression calculation is paused until you go back down below this limit. An audible alarm and a downward pointing red arrow in front of the ceiling depth value indicate unsafe decompression.

    If you ignore the alarm and stay above the safe margin for three minutes, Suunto EON Steel Black locks the algorithm calculation, and decompression information will not be available anymore on the dive. See Algorithm lock.

Decompression display examples

Suunto EON Steel Black shows the ceiling value always from the deepest of these stops.

In the below display, the ceiling depth is set to 17.1 m and the diver is currently at 17.1 m. White arrows beside the ceiling depth value show the diver is inside the decompression window.

deco display same depth

The following example shows that the decompression ceiling depth is at 15.2 m and diver is at 14.7 m. Diver is still inside the decompression window but above the optimal limit. A yellow downward pointing arrow indicates the diver is recommended to descend to be at optimal depth.

deco display yellow

The following example shows that the decompression ceiling depth is at 12.4 m and diver is at 11.0 m. The diver is outside of the decompression window and must descend. A red arrow and an alarm sound prompt the diver to dive deeper and the ceiling depth is indicated in red.

deco display red


When you dive with the Suunto Fused™ RGBM 2 algorithm and the ceiling is broken for more than 3 minutes, the decompression algorithm gets locked.

With decompression stops, in the continuous ascent mode the ceiling is constantly decreasing while you are near the ceiling depth, providing continuous decompression with optimum ascent time. While in the stepped ascent mode, the ceiling is the same for a specific time and then moves upwards 3 m (9.8 ft) at a time.


It is always recommended to keep close to the decompression ceiling when ascending.

Ascent time is always the minimum time needed to reach the surface. It includes:

  • Time required for deepstops
  • Ascent time from depth at 10 m (33.0 ft) per minute
  • Time needed for decompression

When diving with multiple gases, remember that the ascent time is always calculated with the assumption that you use all the gases found in the Gases menu. Always check that you have only the gases for your current planned dive defined before you dive. Remove the gases that are not available for the dive.


YOUR ACTUAL ASCENT TIME MAY BE LONGER THAN DISPLAYED BY THE DIVE COMPUTER! The ascent time will increase if you: (1) remain at depth, (2) ascend slower than 10 m/min (33 ft/min), (3) make your decompression stop deeper than at the ceiling, and/or (4) forget to change the used gas mixture. These factors might also increase the amount of breathing gas required to reach the surface.

Last stop depth

You can adjust the last stop depth for decompression dives under Dive settings » Parameters » Last stop depth. There are two options: 3 m and 6 m (9.8 ft and 19.6 ft).

By default, the last stop depth is 3 m (9.8 ft). This is the recommended last stop depth.


This setting does not affect the ceiling depth on a decompression dive. The last ceiling depth is always 3 m (9.8 ft).


Consider setting the last stop depth to 6 m (19.6 ft) when you dive in rough sea conditions and stopping at 3 m (9.8 ft) is challenging.

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