The “Undeserved Hit” Conversation Nobody Likes Having
Benjamin Hadfield May 25, 2026
The “Undeserved Hit” Conversation Nobody Likes Having
I hear it all the time.
A diver gets decompression sickness, or what we commonly call DCS, and somewhere in the conversation, somebody says:
“Well, they followed their computer. It must have been an undeserved hit.”
Now, I am going to say something that may irritate a few people, but it needs to be said.
Most “undeserved hit” stories are not nearly as undeserved as people want them to be.
That does not mean the diver was reckless. It does not mean they were stupid. It does not mean they intentionally ignored their training. What it usually means is that the diver believed the dive computer was a magic permission machine instead of what it actually is: a mathematical model strapped to your wrist, making its best guess based on limited information.
Dive computers are incredible tools. I love them. I teach with them. I rely on them. I also do not worship them.
Divers Alert Network puts this very clearly: decompression models predict outcomes, but they do not guarantee them, and the fact that a dive stayed within a computer’s limits does not automatically make a DCS case “undeserved.” Algorithms are guidance, not immunity.
That sentence alone should be taped to the inside of every dive computer box.
Your dive computer knows your depth, time, ascent rate, breathing gas, and algorithm settings. Some computers may know water temperature, some may estimate heart rate or workload, and some may look very impressive while doing it. But your computer does not truly know how dehydrated you are, how poorly you slept, how much current you fought, how stressed you were, whether you were cold during decompression, whether you were sick last week, whether you have an undiagnosed medical issue, or whether you spent the previous night treating rum punches like a competitive event.
It does not know that you are 25 in your mind but 52 in your knees.
It does not know that your “easy dive” involved pulling yourself along a wreck in ripping current while pretending you were relaxed because your buddy looked calmer than you did.
It does not know that your surface interval consisted of a protein bar, half a bottle of water, and arguing with your gear bag.
And because it does not know those things, you have to know them.
DCS Is Not Always a Rule Violation
Let’s be fair and accurate.
DCS can happen even when a diver follows accepted guidelines. DAN notes that almost any dive profile can result in decompression illness because known and unknown risk factors can affect an individual diver’s probability of injury. During a dive, tissues absorb inert gas, and if pressure is reduced too quickly for that diver and that exposure, gas can come out of solution and form bubbles. That can happen after obvious violations, but it can also happen after dives that appear acceptable on paper.
That is the uncomfortable truth.
But here is the other uncomfortable truth: “I followed my computer” is not the same thing as “I made a conservative decision.”
Following a computer set to aggressive limits, while tired, dehydrated, cold, doing repetitive dives, with short surface intervals, after travel, in current, while pushing NDLs, is not conservative diving. It is just organized optimism with a battery.
There are legitimate medical factors that can increase DCS susceptibility. A patent foramen ovale, or PFO, is one example. DAN reports that PFO is associated with certain neurological and cutaneous DCS presentations, and divers with PFO have increased relative risk, although the absolute risk remains low for many divers. Routine screening for every diver is not generally indicated, but testing may be considered after repeated DCS events with certain neurological, spinal, inner ear, or skin manifestations.
So yes, there are real medical wild cards.
But for the everyday diver, the bigger issue is often not a mysterious curse from Neptune. It is risk stacking.
One small risk factor may not be a big deal. Five small risk factors piled on top of an aggressive computer setting can become a very different animal.
That animal, by the way, has teeth.
The Nitrogen Tax
I like to explain decompression stress with what I call the nitrogen tax.
Every dive creates a bill. Depth, time, gas choice, ascent rate, workload, temperature, and repetitive exposure all add charges to the account. Your body has to pay that bill during ascent, during stops, and after the dive.
When you set your dive computer to a more aggressive conservatism setting, you are not making the tax disappear. You are just choosing to pay it with less money in the account.
Think about your mortgage. If your mortgage is $3,000 and you keep exactly $3,000 in the bank, you are technically fine — until something changes. A delayed paycheck. A flat tire. A surprise expense. Suddenly, that “perfectly calculated” plan bounces.
Diving works the same way, except instead of overdraft fees, we are talking about bubbles, oxygen, chambers, and phone calls nobody wants to make.
A little extra margin gives you latitude.
And in diving, here is the truly annoying part: you never know your exact balance.
Today you may be young, hydrated, rested, fit, warm, and relaxed. Tomorrow you may be older by one day, sleep-deprived, slightly sick, cold, stressed, and pretending that airport coffee counts as hydration. Your dive computer may treat those two days the same.
Your body may not.
What Your Dive Computer Actually Knows
A dive computer is very good at tracking the things it can measure.
It tracks your depth.
It tracks your time.
It tracks your ascent rate.
It tracks your breathing gas if you set it correctly.
It calculates inert gas loading and decompression status using a model.
That is useful. That is powerful. That is why modern diving is better with computers than without them.
But the computer is not measuring the full human being wearing it.
DAN has pointed out that decompression stress is driven primarily by the dive profile, but thermal state and exercise can play important roles, and current dive computers do not meaningfully integrate those factors into decompression risk calculations.
That matters.
A warm, relaxed diver drifting along a reef and a cold, overworked diver fighting current on the same depth/time profile are not necessarily carrying the same decompression risk.
The computer may show the same NDL.
The bodies may not be having the same conversation.
Gradient Factors, Explained Without Needing a Whiteboard and a Nervous Breakdown
Many technical dive computers use the Bühlmann decompression model with gradient factors. That sounds fancy, but the basic concept is manageable.
A decompression model estimates how much inert gas different theoretical tissue compartments can tolerate at different pressures. Gradient factors allow the diver or instructor to add a margin by using only a percentage of the model’s allowed limit.
Gradient factors are usually shown as two numbers, such as 45/70, 45/80, or 50/85.
The first number is GF Low.
The second number is GF High.
GF Low influences where your first decompression stop begins. A lower GF Low generally creates deeper first stops.
GF High influences how close to the model’s maximum tolerated limit you are allowed to be near the surface. A lower GF High generally creates more conservative surfacing pressure and often more shallow decompression time.
The key phrase is “generally,” because decompression is not a bumper sticker.
A common mistake is thinking that “lower is always safer” in every possible way. Lower GF High usually adds shallow-water conservatism, which is often useful. But driving GF Low extremely low can create very deep stops, and modern decompression discussions are more cautious about assuming deep stops are automatically better. The research and expert discussion around deep stops is complex, and the practical takeaway is simple: do not randomly copy internet gradient factors without understanding what they do.
That includes the guy online who says, “I use 10/95 and feel great.”
Fantastic. My dog also feels great after eating things from the trash. That does not make him a nutritionist.
Conservative Settings Are Not a Punishment
Some divers treat conservative settings like a penalty.
They say things like:
“I don’t want my computer to be too conservative.”
“I don’t want to lose bottom time.”
“My buddy gets more time than I do.”
“This thing is too cautious.”
“I felt fine last time, so I changed it.”
That last one is the trap.
Feeling fine after a dive is good. There is no proof that your settings are optimal.
DCS risk is probabilistic. That means a profile can work many times and still not be a good idea. You can run a red light and make it through the intersection. That does not make red lights optional. It just means physics, traffic, and luck had a brief meeting and decided not to ruin your morning.
The question is not, “Can I get away with this?”
The question is, “How much margin do I want when the conditions are not perfect?”
That is what conservatism is. It is a margin.
It is not a weakness. It is not fear. It is not being less advanced.
It is understood that the ocean does not care about your certification card.
The “Felt Fine” Problem
One of the worst ways to choose your gradient factors is this:
“I felt good after that dive, so I think I can make my computer more aggressive.”
No.
That is like saying, “I drove home after four hours of sleep and did not crash, so next time I’ll close one eye.”
How you feel after a dive matters, but it is not reliable enough by itself. Fatigue, soreness, dehydration, seasickness, anxiety, workload, exertion, poor sleep, sun exposure, and mental expectation can all distort how we interpret our condition.
Sometimes divers feel bad and blame DCS when it may be dehydration, exertion, seasickness, or poor sleep. Sometimes divers feel “just a little off” and dismiss symptoms they should take seriously. DAN lists unusual fatigue, joint pain, tingling, numbness, dizziness, rash, weakness, confusion, and difficulty urinating among possible DCS signs and symptoms; suspected cases should be treated seriously, with oxygen first aid and dive-medicine consultation.
So yes, log how you feel.
But do not let “I felt fine” become your only data point.
Your feelings are part of the evidence. They are not the judge, jury, and decompression planner.
When You Should Add More Conservatism
There are times when adding margin is simply smart.
Not dramatic. Not paranoid. Smart.
Consider using more conservative settings, adding longer shallow stops, increasing surface intervals, reducing depth or bottom time, or limiting repetitive exposure when any of the following apply:
You have not been diving for a few months and are getting back in the water.
You are doing repetitive vacation dives, especially multiple days in a row, while trying to set a personal record for “most bubble time while pretending sunscreen is a food group.”
You traveled recently, slept poorly, or are still mentally and physically tired from the trip.
You were up late the night before.
You are dehydrated or even questionably hydrated.
You are diving cold water or got cold during the dive.
You expect current, surge, low visibility, heavy gear, a long surface swim, or task loading.
You are diving deeper than usual.
You are doing decompression dives, overhead training, wreck penetration, cave, trimix, rebreather, or anything where “just go up” is not a complete emergency plan.
You are older than you used to be, which applies to everyone unless you have discovered time travel and are selfishly keeping it from the rest of us.
You are recovering from illness, injury, stress, or a long break.
You are diving after a hard workout or planning strenuous activity after diving.
You are doing multiple consecutive days of diving.
You feel pressured to keep up with someone else’s computer.
The CDC also lists depth, time, ascent rate, altitude exposure after diving, cold water, currents, low visibility, wave action, repetitive dives, multiple dive days, overhead environments, strenuous exercise, and dehydration as risk factors that can increase DCI risk.
That is not a short list.
And that is the point.
Conservatism is not just about the dive. It is about the diver, the day, the conditions, and the plan.
How to Choose Your Conservative Setting or Gradient Factors
Here is the part everyone wants: “Benjamin, just tell me the numbers.”
No. NOPE. NOT GONING TO DO IT!
Not because I am trying to be difficult, although I do enjoy that recreationally. It is because choosing settings without context is exactly the problem.
The correct setting depends on the diver, the dive, the computer, the algorithm, the gas, the training level, the environment, the team, and the acceptable risk level.
But I can give you a framework.
1. Start With Training, Not Internet Settings
If you do not understand what your conservative setting or gradient factors do, do not change them based on a forum, a boat conversation, or a TikTok comment from somebody named “DecoWarrior77.”
Start with the manufacturer's default, your agency standards, and your instructor’s guidance.
If you are in technical training, your gradient factors should be part of the course discussion. You should understand what they change, why you are using them, and how they affect your decompression obligation.
At Stuart Scuba, this is exactly the kind of conversation we have in technical diving training. We are not just teaching you to follow numbers. We are teaching you to understand what those numbers are trying to represent.
That distinction matters.
2. Understand What Your Computer’s Conservatism Setting Actually Changes
Not all computers adjust conservatism the same way.
Some computers use gradient factors directly.
Some use “low, medium, high” conservatism settings.
Some adjust NDLs.
Some modify decompression obligations.
Some add safety factors that are not fully transparent to the user.
Read the manual. I know. That sentence hurts.
But your dive computer is life-support-related equipment. If you can spend forty minutes comparing the color of bolt snaps online, you can read the section that tells you how your decompression settings work.
3. Treat GF High as a Major Surfacing-Risk Lever
For most divers using Bühlmann with gradient factors, GF High deserves special attention because it affects how close the model allows you to get to the theoretical limit near the surface.
A lower GF High means more conservatism at the end of the ascent and the length of your final stop.
That last stop matters. It is often where meaningful off-gassing happens.
If you are tired, cold, repetitive diving, or pushing exposure, GF High is often the number that divers and instructors look at first when adding conservatism.
4. Do Not Abuse GF Low
GF Low affects the depth of the first stop. Lower GF Low usually means deeper initial stops.
For years, many technical divers believed deeper stops were automatically better. The modern view is more nuanced. Very low GF Low values may create deeper stops that are not beneficial, especially when they increase inert gas loading in slower tissues.
Translation: do not assume that 20/70 is automatically “safer” than 50/70 just because the first number is lower.
Decompression is not a limbo contest. The goal is not “how low can you go?”
The goal is efficient, appropriate decompression for the dive.
5. Make the Setting Match the Dive, Not Your Ego
If your plan is a shallow single reef dive in warm water, with no current, after a good night’s sleep, with a long surface interval, your setting choice may be different from a deep wreck dive in current after three days of repetitive diving.
That should be obvious.
But divers often want one magic setting forever.
There is no magic setting.
There is only a thoughtful diver making a reasonable choice with the information available.
6. Keep the Team Compatible
If you are diving as a team, your decompression strategy needs to be compatible.
If one diver is on aggressive settings and one diver is on highly conservative settings, you may end up with mismatched obligations, confusion, or pressure to ignore one computer.
That is bad team diving.
Before the dive, discuss (BTW, this is the most underutilized skill in diving):
What algorithm is everyone using?
What gradient factors or conservatism settings are being used?
What is the planned maximum depth and time?
What is the turn pressure or gas plan?
What is the minimum gas?
What is the ascent strategy?
What stops are planned?
Whose computer controls the dive if there is disagreement?
What is the contingency if one computer creates more obligations?
These conversations are not boring. They are the adult part of diving.
The fish will still be there after the briefing.
Probably.
Fish are terrible at scheduling.
The Dive Log as Your Black Box
This is the deeper answer, and it is the part that not enough divers do.
Your dive log should be more than depth, time, temperature, and gas.
That is not a dive log. That is a receipt.
A good dive log should function like a black box. It should help you reconstruct not only what happened underwater, but what was happening to the diver before, during, and after the dive.
If you want to make smarter decisions about gradient factors and conservative settings, you need better data.
Start recording:
Dive site
Date and time
Computer used
Algorithm
Conservatism setting or gradient factors
Gas mix
Average depth
Maximum depth
Bottom time
Total run time
Ascent rate
Safety stop or decompression stops
Surface interval
Number of dives in previous 24 and 48 hours
Water temperature
Exposure protection
Whether you were cold at depth, during ascent, or after surfacing
Current, surge, visibility, and sea state
Workload level
Stress level before the dive
Stress level during the dive
Task loading
Any equipment problems
Gas consumption
Hydration before and after
Alcohol the night before
Sleep quality
Travel fatigue
Food intake
Exercise before or after diving
Post-dive symptoms
Post-dive fatigue level
Mood and mental clarity
Whether you had to lift heavy gear, climb a ladder in rough seas, or help someone else
Whether you felt pressured, rushed, or behind the team
That may sound like a lot.
Good.
Diving is a lot.
The more serious the dive, the more serious the logging should be.
For my daily stress and health, I use tracking tools to watch trends in sleep, activity, and stress. Use Evidation, a smartwatch, a notebook, your phone, wetnotes, a spreadsheet, or a napkin you promise not to lose. The specific tool matters less than the habit.
The key is to stop relying on hopeful memory.
Because “I think I felt fine last time” is not data.
It is a campfire story with nitrogen in it.
A Simple Personal Risk Color System
Here is a practical way to use your log and your brain together.
Before the dive, assign yourself a personal risk color.
Green Day
You slept well.
You are hydrated.
You feel healthy.
You are not rushed.
Conditions are familiar.
The dive is within your normal range.
You have good surface intervals.
You are not stacking repetitive exposure.
You are mentally calm.
On a green day, your normal conservative setting may be appropriate.
Yellow Day
You slept poorly.
You traveled recently.
You are doing repetitive dives.
Conditions are harder than usual.
There is current or cold.
You are mildly stressed.
You are diving near the edge of your normal comfort zone.
You had a short surface interval.
You are not feeling bad, but you are not at your best.
On a yellow day, add margin. Reduce planned bottom time, increase surface interval, use a more conservative setting, extend shallow stops, or simplify the dive.
Red Day
You feel sick.
You are exhausted.
You are dehydrated.
You are hungover.
You are anxious or distracted.
Conditions are beyond your comfort or training.
You are being pressured.
You had symptoms after a previous dive.
You cannot focus.
You are trying to convince yourself it is fine.
On a red day, the best conservative setting may be dry clothes and lunch.
There is no shame in calling a dive.
There is shame in needing a chamber because you were afraid to look uncool on a boat full of people who were mostly worried about their own mask fog anyway.
Stories From the Real World
The Vacation Hero
There is always one.
They arrive at the resort with a brand-new computer, a brand-new rash guard, and the energy of a golden retriever in a bait shop.
Day one: two dives.
Day two: three dives.
Day three: “Let’s do the deep wreck.”
Day four: “Night dive?”
Day five: “Why am I so tired?”
They are not doing anything wildly outside the rules. Their computer still clears them. But they are stacking repetitive exposure, sun, dehydration, poor sleep, boat rides, excitement, and sometimes alcohol.
That is not one risky decision. It is twelve tiny decisions wearing a trench coat.
A more conservative approach would be longer surface intervals, fewer dives on the heavy days, more hydration, real rest, and not treating the NDL like a countdown timer in a video game.
The “I Haven’t Been Diving in Six Months” Dive
This diver is certified, experienced, and genuinely capable.
But the first dive back after a break is not the time to push depth, current, new equipment, a camera, a scooter, and a dramatic personal comeback story.
Skill rust creates stress. Stress increases workload. Workload changes breathing, buoyancy, awareness, and decompression stress.
The conservative choice is not just a computer setting. It is choosing an easier dive, getting comfortable again, and leaving some ego in the truck where it belongs.
The Deep Wreck With Current
South Florida diving can be beautiful, but it can also remind you that the ocean is not a swimming pool with fish stickers.
A diver drops on a wreck, hits more current than expected, works harder than planned, burns more gas, gets colder than expected during ascent, and then climbs a ladder in sporty seas with doubles or stages.
The computer may only see the profile.
The diver lived the workload.
That is exactly where conservatism matters.
Practical Guidance for Recreational Divers
If you are a recreational diver using a standard recreational computer, here are some simple rules.
Do not set your computer to the most aggressive mode just because you want more bottom time.
Do not chase your buddy’s NDL.
Do not ride the NDL to zero on every dive.
Do not skip safety stops just because they are not mandatory.
Be especially cautious on dives deeper than 100 feet, repetitive dives, cold dives, current dives, or dives after poor sleep or travel. DAN recommends recreational divers dive conservatively, avoid approaching no-decompression limits, and be especially cautious when diving deeper than 100 feet or under strenuous or cold conditions.
If your computer offers personal conservatism levels, consider using a more conservative level when risk factors stack.
If your computer allows gradient factors and you do not understand them, get training before changing them.
That is not a sales pitch.
Actually, it is a little bit of a sales pitch.
But it is also true.
Practical Guidance for Technical Divers
If you are a technical diver, this conversation gets more serious.
Your gradient factors should be chosen as part of a decompression strategy that includes:
Dive objective
Maximum depth
Bottom time
Gas choices
Oxygen exposure
Narcosis management
Thermal protection
Workload
Team procedures
Bailout or contingency gas
Environmental conditions
Emergency strategy
Surface support
Your recent dive history
Your health and readiness
Technical diving is not about being brave.
Technical diving is about making boring plans so that exciting things do not become catastrophic things.
At Stuart Scuba, our technical diving courses include programs such as Intro to Tech, Advanced Nitrox and Decompression Procedures, Trimix, Helitrox, and Rebreather training. We also support technical diving with gas fill options, including partial pressure fills, stick fills, trimix, oxygen, helium, and EANx fills.
The point is not just to go deeper.
The point is to come back smarter.
The Most Conservative Setting Is Not Always on the Computer
This may be the most important part.
Your computer settings are only one layer.
Other conservative choices may matter just as much or more:
Plan a shorter bottom time.
Use nitrox appropriately while planning within air limits when suitable.
Increase surface interval.
Limit repetitive dives.
Stay warmer.
Work less.
Improve trim and propulsion.
Carry adequate gas.
Ascend slowly and correctly.
Do not sawtooth the profile.
Do not do heavy exercise right after diving.
Hydrate.
Sleep.
Eat real food.
Call the dive when conditions are wrong.
Stop pretending “I’m fine” is a medical evaluation.
If you have a known medical issue, repeated symptoms, unexplained neurological symptoms, or a history of DCS, consult a physician trained in dive medicine. Do not ask Facebook to clear you for decompression diving. Facebook once thought eating detergent pods was a trend. Let’s keep standards higher than that.
What to Do If You Suspect DCS
This article is about prevention, but we need to say this clearly.
If you have unusual symptoms after diving — especially tingling, numbness, weakness, dizziness, unusual fatigue, rash, joint pain, confusion, difficulty walking, difficulty urinating, shortness of breath, or neurological symptoms — take it seriously.
Administer oxygen if trained and equipped to do so. Stop diving. Contact DAN or emergency medical services. DAN states that early oxygen first aid is essential and that suspected DCI cases should involve DAN or a physician trained in dive medicine, even if symptoms appear to improve.
Do not “wait and see” your way into a worse outcome.
DCS denial is common because nobody wants to be the diver who ends the trip.
But the trip is already over if your nervous system is sending you weird text messages.
Answer the phone.
Final Thought: The Computer Is a Tool. You Are the Diver.
Your dive computer is not the captain.
It is not the instructor.
It is not the physician.
It is not the ocean.
It is a tool.
A very good tool, but still a tool.
The real conservative factor is the diver using it.
Choosing gradient factors and conservatism settings is not about finding the magic number that gives you maximum bottom time. It is about understanding the dive, the day, the body, the team, and the consequences.
The aggressive diver asks, “How much time can I get?”
The thinking diver asks, “How much margin do I want?”
That is the difference.
And if you want to learn how to make those decisions with more confidence, come train with us.
At Stuart Scuba in Stuart, Florida, we teach technical diving the way it should be taught: with discipline, humor, real-world context, and a healthy respect for the fact that the ocean does not negotiate. Whether you are looking at Intro to Tech, Advanced Nitrox and Decompression Procedures, Helitrox, Trimix, sidemount, or rebreather training, I would love to help you become a more thoughtful, capable, and conservative technical diver.
Come take tech with Benjamin at Stuart Scuba.
We will talk about gradient factors.
We will talk about decompression.
We will probably make fun of your fin kicks at least once.
Lovingly, of course.
