How to read a dive computer's NDL when conditions change fast

## Understanding NDL No-decompression limits (NDL) tell you how long you can stay at depth before your tissues absorb enough nitrogen to require a decompression stop on ascent. But the numbers your computer shows aren't fixed — they shift based on your ascent rate, your tissue saturation from previous dives, and the dive profile itself. ### When to trust the number For square-profile dives in cool water with conservative algorithms (Bühlmann ZHL-16C with low gradient factors), the NDL displayed is usually accurate. For multi-level dives, especially when you're going shallow-deep-shallow, your computer is doing real work to model your saturation. ### When to be sceptical - After multiple dives in a day, especially if you've been close to the NDL each time - After a flight (cabin pressure changes nitrogen elimination) - If you've been dehydrated or had a long surface interval in heat - If you exerted heavily underwater ### Conservative practice Most instructors in Malaysia and SEA suggest treating the NDL as your soft limit, not your hard limit. Plan to surface with at least 5 minutes of NDL remaining for shore dives, 10+ for boat dives where you might miss your safety stop due to current.