The Core Data Fields
Every dive computer, regardless of brand or price, displays the same essential information during a dive. Learning to read these fields instinctively — without pausing to think — is a fundamental dive skill.
Current Depth
Usually the largest number on the screen, displayed in meters or feet. The computer samples its pressure sensor every second and updates the depth reading in real time. It also records your maximum depth for the dive log.
Dive Time
A running timer that starts when you descend past approximately 0.8–1.2 meters (depending on the model). Some computers display this as minutes only; others show minutes and seconds. This is total bottom time, not a countdown.
No-Decompression Limit (NDL)
The most critical number for safe diving. It tells you how many minutes you can remain at your current depth before the algorithm requires mandatory decompression stops on ascent. When NDL counts down to zero, you are in "deco" — the screen will switch to showing required stop depths and times instead of NDL.
Ascent Rate Indicator
Most computers display ascent rate as a vertical bar graph alongside the depth reading, color-coded from green (safe) through yellow (caution) to red (too fast). Some also display the actual rate in meters or feet per minute. The standard recommended rate is 9–10 m/min (about 30 ft/min).
Temperature
Water temperature, usually displayed in a smaller font. Useful for logging and for identifying thermocline layers.
Safety-Related Displays
Safety Stop Countdown
When you begin your final ascent, most computers trigger a three-minute safety stop at 5 meters (15 feet). The screen displays a countdown timer. This stop is a recommended precaution, not a mandatory deco stop — but you should complete it on every dive.
Deco Stop Display
If you exceed your NDL, the screen switches to decompression mode. It shows the shallowest required stop depth and the time you must spend there before ascending further. Follow every displayed stop precisely.
Alarms and Warnings
Dive computers use audible beeps, screen flashes, and vibration (on some models) to alert you to dangerous conditions: fast ascent rate, low NDL, missed safety stop, low battery, and depth limit warnings. Learn what your specific computer's alarm patterns mean before you dive with it.
Air-Integration Data (If Equipped)
If your computer is paired with a wireless transmitter, additional fields appear:
Tank Pressure: Displayed in bar (metric) or PSI (imperial), showing your remaining air supply.
Gas Time Remaining (GTR): An estimate of how many minutes of air you have left based on your current breathing rate and depth. This number updates dynamically — if you calm your breathing, GTR increases; if you exert yourself, it decreases.
Breathing Rate: Some computers display your air consumption rate, often called SAC (Surface Air Consumption) rate, which helps you monitor your efficiency over time.
Surface Mode Display
Between dives, your computer switches to surface mode and displays:
Surface Interval Timer: How long since your last dive ended. Critical for repetitive dive planning.
Desaturation Time: How long until your body is fully off-gassed to a no-residual-nitrogen state.
No-Fly Timer: How long until it is safe to fly. Typically 12–24 hours after your last dive, depending on the number and depth of dives.
Tissue Loading Bar Graph: Many computers display a visual representation of nitrogen saturation across their tissue compartments, showing which tissues are most loaded.
Practical Tips
Learn your screen layout on land first. Every computer arranges data differently. Spend time in the pool or bathtub familiarizing yourself with where each field appears.
Use the backlight liberally. In low-vis or deep water, hit the backlight button before checking your screen. LED backlights cost minimal battery.
Check your screen every 2–3 minutes. Make it a habit to glance at depth, NDL, and air (if equipped) regularly — not just when you feel like it is time to surface.
Know what "—" dashes mean. When NDL shows dashes or "deco," you have exceeded your no-decompression limit. This changes your ascent from optional safety stop to mandatory decompression.