Divers have to be able to determine with accuracy how much Nitrogen is in their body at any given time. Back in the day, divers used to have to use a dive table to determine this. Pictured left, this dive table would guide a diver through manual calculations to a hardline time limit of how long they could stay at a given depth. This time limit is also commonly referred to as the No Decompression Limit. With a dive table, it didn’t matter if you touched your maximum depth for 2 seconds, 2 minutes or 20 minutes. Your total dive time was pre-determined, unless you did an entirely separate calculation using the table for a multi-level dive. Sound tedious? It is!
For example, if you are planning a 50 foot dive, and you drop your GoPro or light, you can go to 60 feet to pick it up briefly. When diving with a table, you would have to calculate for a 60 foot dive. On the other hand, dive computers are a foot by foot No Decompression Limit calculator. So if you come back shallower, it will recalculate and extend your No Decompression Limit to reflect your current depth. Remember to check your computer constantly to monitor both your current depth and your current No Decompression Limit. Once you go beyond it, you have now entered Decompression diving and have placed a virtual ceiling over yourself. Now you must make mandatory stops as you ascend. These stops can sometimes be 10 minutes to hours at a time, and if skipped, will likely result in Decompression Illness.
Unplanned Decompression is dangerous.
Decompression training is not covered in standard Open Water or even Advanced coursework. The recreational diver would be wise to avoid these technical challenges.
The bar graph is a real time display of how much Nitrogen you have in your body. The bar graph takes a longer time to change than the foot by foot No Decompression Limit. Checking the Nitrogen bar can help you decide if you want to do a longer safety stop or surface interval to reduce risk.
Your total dive time after repetitive dives (multiple dives within 24 hours) will play a factor in all the calculations. Keep track of your total dive time.