The end of the dive is where risk concentrates
During a dive your body takes up nitrogen, and during the ascent it starts to release it. If pressure drops faster than your tissues can off-gas, bubbles can form, which is what causes decompression sickness. That is why the way you finish a dive deserves as much attention as the way you plan the deepest part of it.
Three habits make the biggest difference: a slow ascent, a safety stop on every dive, and enough time on the surface before the next dive or a flight.
Ascend slowly
Most training agencies and dive computers now recommend ascending no faster than about 9 to 10 meters per minute. Your computer will warn you if you go faster. A useful reference is to rise no faster than your smallest bubbles, although with modern computers it is easier to simply watch the ascent rate indicator.
The final ten meters are where the pressure changes most in relative terms, so slow down even more as you approach the surface. Good buoyancy control is what makes this possible: vent your BCD in small amounts as you rise, rather than letting the expanding air carry you up.
Make a safety stop on every dive
A safety stop is a pause of three to five minutes at around 5 meters at the end of a dive. It is not a required decompression stop on a no-decompression dive, but it gives your body extra time to release nitrogen, and studies have shown it reduces the bubbles detected after diving. It also gives you a calm moment to check your buddy, your gas and your surroundings before you reach the surface.
Treat it as part of every dive, including shallow ones, and add a little extra time after deep dives, long dives, repetitive dives or a fast ascent. If you have little gas left, a shorter stop is better than none, but plan so that does not happen: reaching the stop with a comfortable reserve is part of a good dive plan.
In a current or open water, a surface marker buoy deployed during the stop lets the boat follow you, and holding a line or hovering together with your buddy makes it easier to keep a steady depth.
Surface intervals
The time between surfacing from one dive and descending on the next is your surface interval. During it you keep releasing nitrogen, and your computer tracks how much remains, which is why your second dive of the day shows shorter no-decompression limits than the first.
Follow your computer, and treat its numbers as limits rather than targets. A longer interval, at least an hour between dives, gives you more margin. Drink water, stay warm and avoid heavy exertion such as hauling gear up the beach right after a dive.
Plan the day so dives get shallower as they go on. A deep first dive followed by shallower ones keeps your no-decompression time comfortable.
Flying after diving
Cabin pressure in an airliner is lower than at sea level, so flying too soon after diving raises the risk of decompression sickness. Widely used guidelines recommend waiting at least 12 hours after a single no-decompression dive and at least 18 hours after multiple dives or several days of diving. Many divers simply leave a full day without diving before their flight.
Your dive computer usually shows a no-fly time. Use the longer of that time and the guideline, and remember that driving over a high mountain pass counts as altitude too.
Frey Dive keeps the start time and bottom time of each dive in your log, so it is easy to look back at what you did that day when you plan the trip home.