How to Read the DECO 2000 Dive Table: A Worked Example

What is on the DECO 2000 table?

DECO 2000 is an air decompression table by Dr. Max Hahn, published by the German diving federation VDST and taught in CMAS courses. The front of the card is split into depth blocks from 12 m (40 ft) down, in 3 m steps. Each block shows its no-stop limit, a column of bottom times, the minutes of decompression owed at 12, 9, 6 and 3 m, and a group letter between B and G.

The back continues to the deeper blocks, down to 42 m (138 ft), and holds three more things: the surface interval table, the residual nitrogen times for a repetitive dive and a no-fly column. On the printed card, white rows are no-stop dives and shaded rows need decompression. Our DECO 2000 table page shows both sides in one place.

Step 1: Round the maximum depth up, never down

Take the deepest point of the dive, not the average, and move to the next deeper depth on the table. 19 m becomes 21 m. 22.5 m becomes 24 m. A depth that sits exactly on the table, such as 18.0 m, uses its own block.

The table assumes a rectangular profile. It has no idea you spent most of the dive on a 12 m reef top after a quick look at 22 m, so it charges the whole bottom time at 22 m, rounded to 24. That is one reason the table and a dive computer disagree after a multilevel dive: as DAN's review of dive computer validation puts it, the computer calculates from the actual depth instead of rounding to the next deeper one.

Anything shallower than 12 m is read on the 12 m block. Anything deeper than 42 m is off the card. Scuba Brief treats 30 m (100 ft) as the recreational limit and shows the deeper blocks for training use only.

Step 2: Check the no-stop limit for that depth

The figure printed under each depth is its no-stop limit: the longest bottom time that still allows a direct ascent with no mandatory stops. It is valid only for a first dive, with no nitrogen left over from an earlier one. The table below lists the limits from 15 m down, the group letter you get on the limit row and what the next row costs.

The 12 m block is the exception. Its limit is 140 minutes, but its time rows end at 108 minutes, which already puts you in group G.

DECO 2000 is on the short side. For 18 m (60 ft), a comparison on divetable.info lists 45 minutes for DECO 2000, 56 for the PADI RDP, 55 for NAUI and 50 for both SSI and DCIEM. Treat the limit as a ceiling rather than a target. Taucherpedia's advice is to start the ascent well before you reach it.

Step 3: Round bottom time up and read the stops

Bottom time runs from the moment you leave the surface to the moment you start the final ascent, so the descent counts. Round it up to the next time row in your depth block and read across that row.

The four stop columns are ordered deepest first: 12, 9, 6 and 3 m. An empty cell means no stop at that depth. A dive to 30 m for 39 minutes, for example, owes 1 minute at 9 m, 7 minutes at 6 m and 17 minutes at 3 m, and ends in group G. That is 25 minutes of stops after a 39 minute bottom time.

Stops cost gas as well as time. divetable.info works through a dive to 37 m for 16 minutes: the table reads it as 39 m and 18 minutes, with 3 minutes at 6 m and 7 minutes at 3 m, group F. That adds about 10 minutes of breathing to the dive, and the gas plan has to cover them.

A safety stop is a separate thing. Taucherpedia recommends 3-5 minutes at 3-5 m on every dive and, when the table already requires a 3 m stop, extending that stop by the safety stop time.

Worked example: 22.5 m for 24 minutes

A dive to a maximum of 22.5 m (74 ft), with the ascent starting 24 minutes after leaving the surface, reads as 24 m and 27 minutes: 2 minutes at 3 m, group E. Round the depth down instead and the same dive looks like a no-stop dive.

The comparison below shows how thin the margins are. One minute less on the bottom would have made it a no-stop dive. Five minutes less would have dropped it to group D. The DECO 2000 planner gives the same readings for this profile and flags the stop. Step by step:

• Depth: 22.5 m is not on the card, so use the 24 m block. Not 21 m.
• No-stop limit at 24 m: 23 minutes. You are one minute over it, so expect a stop.
• Time: 24 minutes rounds up to the 27 minute row.
• Stops: the 27 minute row shows 2 minutes at 3 m and nothing deeper.
• Group letter: E.
• Ascent: at 10 m per minute the climb to 3 m takes about 2 minutes. Hold 3 m for the 2 required minutes, then add your safety stop time.

Step 4: What the group letter controls

The letter is a rough measure of the nitrogen the model assumes is still in your body when you surface. B is the lightest load on the card and G the heaviest. You need it for the back of the table, both for a repetitive dive and for the no-fly column, so write it down with maximum depth, bottom time and surfacing time. Our guide on how to log a dive covers the rest of the entry.

The no-fly column is where DECO 2000 and current medical guidance part ways. The card asks for 4 hours after a group B dive and 16 hours after group E. DAN's consensus guideline is at least 12 hours after a single no-decompression dive and substantially longer than 18 hours after a dive with required stops. The CDC Yellow Book gives 24-48 hours for that case. Our worked example is a group E dive with a stop, so the card's 16 hours falls short of both. Use the longer figure.

Altitude range and the 10 m per minute ascent

The standard DECO 2000 card is valid from sea level to 700 m (2,300 ft). Lakes higher than that need an altitude table, because the atmospheric pressure at the surface is lower. German club material lists a second DECO 2000 table for 701-1500 m, and divetable.info notes that the table also comes in Nitrox32 and Nitrox36 versions and in a set for mountain lakes. No amount of careful rounding fixes a sea-level card used at 1,000 m.

Altitude also matters after the dive. Taucherpedia applies the no-fly time to trips over mountain passes too. The reason is the same as for flying: lower ambient pressure, which in an airliner cabin drops to about 0.75 bar.

Every stop time assumes an ascent no faster than 10 m per minute. Other tables were built around other rates: divetable.info lists 18 m per minute for the PADI RDP and 9 m per minute for NAUI, which is one reason their numbers do not transfer to DECO 2000. The VDST calculation parameters listed by Tauchverein Delphin budget ascent time from the maximum depth rounded up to the next 10 m, so a climb from 21 m counts as 3 minutes. Taucherpedia also asks for a slower 6 m per minute over the last 10 m. For gas, our gas planner budgets its reserve with an ascent of 9 m per minute, slightly slower than the table.

Common mistakes when reading the table

Most reading errors come from rounding the wrong way or feeding the table the wrong numbers. Each one below turns a correct table into a wrong answer.

• Rounding to the nearer row. Depth and time both round up, even by a fraction.
• Using the average depth from a computer log. The table needs the maximum.
• Starting the clock on arrival at the bottom. Descent time is bottom time.
• Estimating between rows. 25 minutes at 21 m is read on the 26 minute row, never guessed between 21 and 26.
• Treating the limit row as a safe target. At 18 m, 45 minutes is a no-stop dive and 46 minutes is read on the 55 minute row, with 4 minutes at 3 m.
• Ignoring cold and hard work. Taucherpedia's German edition says to use the next longer time row after cold water or a short burst of exertion, and 1.5 times the real bottom time after sustained hard work. divetable.info suggests moving one depth block or one time row further for the same reasons.
• Planning a repetitive dive with the limits on the front of the card. Those limits assume no residual nitrogen. A second dive starts from the back of the table.