What's in a log - each section
A dive log book is used by a scuba diver to record the details of dives they have done. This serves many purposes that are both safety focused and personal.
From a purely personal view point, as you progress through your training you should keep a close eye on your air consumption, weighting, and use of equipment. Seeing how you improve and react to different diving conditions and events will help you become an efficient, and safe diver. Only if you log these down will you remember them. Additionally, in your early days, when you go on holiday you should expect to take your log book and certification cards to prove your competence to go diving. A dive center will want to see proof that you can handle advanced diving conditions before they take you onto a fast current drift dive!
As divers progress, the log book changes from a fact based learning log (how much weight did I use when I was in my 3mm shorty etc.) to more of a journal. It's true that a number of very competent and experienced divers do not keep a log, but a great number of divers still do, and now they are using it to help them remember the great dives from the last holiday. When you spend all that money and time (24 hours underwater in a typical 2 week diving holiday), it can be great to be able to open your log book and jog your memory of the experience. Having said that, even experienced divers are in situations where they can learn more about becoming a safe diver or are using a new piece of kit and want to monitor how it affects their diving and safety. The safety side of your log book should never really go away!
At the other end of the spectrum, instructors and commercial divers (bell diving on oil rigs, filming documentaries, police, maintaining swimming pools etc.) have an extra set of needs for a log book system. Here they need to satisfy local regulatory requirements (like the HSE diving at work regulations in the UK) because they have to show they have taken extra steps to ensure both their own and others safety.
So, what does each section do and how should they be used...
This just contains basic information about the date, time and location of the dive. It may also include a running dive number and for some commercial operations it should also include details of the company the dive was being carried out for.
One of the more important sections for safety. The bare minimum recorded should be bottom time (does not include your safety stop time - this is separate), the maximum depth you reached, and the air you entered and left with. If this is your second dive of the day it should also include your surface interval. If you get the bends after a dive, this information will help a diving doctor or hyperbaric technician with their assessment.
Optional things for recreational divers include your average depth, the time you entered, and your nitrogen saturation levels both before and after a dive. This is if you have a dive computer, which most of us do. If you do not have one of those then you must use your log page and diving tables to do a more detailed calculation and record of your profile and final nitrogen saturation. Getting into Nitrox diving adds in the necessity to calculate your final oxygen loading after a dive.
If you are in the specialist area of Closed Circuit Rebreathers or technical diving then your profile takes on much greater complexity. Here, you will be including such things as the different gas mixes you used at what depths and the state and condition of your technical breathing kit.
For most people, the most important piece in this is the weight used. This (coupled with the record of what you were wearing) will help you plan what weight you should take on your next dive. What you were wearing covers the type and size of cylinder (aluminium weighs less than steel) and the exposure protection you will want to use (neoprene is bouyant stuff). Being correctly weighted is one of the biggest things to influence relaxed and efficient diving and so making sure you achieve low air consumption and enjoy the dive. Optional extras in this section include details of the camera equipment you used if you are into underwater photography.
Not so important for some, the conditions section helps you remember more about the experience. Temperature can be a useful record when it is coupled with your exposure protection; it can help you plan what to take on your next holiday. Visibility can tell you whether you should bother going back!
Space to write down anything you want! In our standard logs you get a place to record the fish encounters which is split off into another section in our nature logs. In particular, it's a great idea to record how you felt, temperature wise. If you are too cold then this will both affect your enjoyment and in those really long dives sorely test your kidneys! If you note down how you felt and compare it with the sea temperature and exposure protection you used you'll be better prepared for the next dive.
If you are heavily into underwater photography or video, you may want to record details of your photos shot by shot to try and improve your quality.
Most divers like seeking out the unusual or rare fish encounter! This is really a section that is more journal like than factual dive log. This is so you can remember when you swam with Whale Sharks or saw a Sun Fish, or just how many lion fish you saw this time.
If you really want to remember the high points from a dive there is no better way than to draw a simple map of your dive and mark on the good bits! Keeping it simple is the key and just putting on the main memories or events. Later on you will be amazed how many memories come flooding back with the visualisation clues you have given yourself.
Instructors should keep a record of who they have been teaching in a dive and what subjects they have covered. Mainly to cover their regulatory requirements, it also acts as a good reminder for instructors who are in the middle of a training program and want to check what a particular student has completed so far.
The validation section keeps a running total of your overall bottom time in the water (useful to show to dive centres when you go on holiday), as well as any validation signatures and log book stamps.
Different sections from the above get put together into overall designs depending upon your needs, standard logs tend to have a bit of everything, whilst nature and photo based logs expand on some areas to give you more detail to write about the things you like. Instructor logs get the student sections included.
Of course, for some people the off the shelf designs are never quite right and they wish they could design their own...