Commercial/military tables worked. but they weren't ideal. In 1988, DSAT (Diving Science & Technology) introduced the Recreational Dive Planner (RDP) which were the first dive table, designed for planning and making no decompression recreational dives. They were the first (and at this writing. still the only) such tables validated by test dives by volunteer recreational divers - men, women, younger. older, etc. 

This remains one of the largest and most extensive decompression tests in recreational diving. Distributed by PADI, the RDP quickly became (and remains) the world's most popular dive tables: quite a few popular dive computers even employ 1ZDI' teat data in their electronic decompression models.

It's available in a Table(conventional) format, and in The Wheel (circular slide rule) format, in both metric and imperial versions. For divers accustomed to conventional tables, DSAT developed The Wheel. To simplify use and to make multilevel diving possible without a dive computer 'more about multilevel diving in a moment. MAT developed The Wheel. You'll he learnig to use one or the other as part of this course - you should know which already.

Dive computers do the same job as dive tables, and they do it in the same way - by using a model to determine how much nitrogen you theoretical have in your body. They're neither more nor less valid than dive tables, ,so don't let the electronics, lights, beeps and digital displays impress you. 

The difference between a dive table and a dive computer is this: to be workable on a piece of plastic, a dive table uses a series of enough approximations for possible dives into which You fit Your dive. whereas a dive computer uses a depth gauge, timer and software to write a custom dive table for your exact dive. Throughout the dive. your computer updates this "custom table" as you change depth. constantly showing you how much no stop dive time you have left.