For all diver, you just not have to be good underwater but also understand the theory about diving it self. I'll give a good link for learn and reading.
Basic of diving, a must have for all kind of diver whether you are a sport scuba diving or a hard hat commercial diving this US Navy Diving manual will help you with complete guide with depth table for decompression.
US NAVY Diving manual Rev.6 April 2008
For Commercial diver that need handbook for cutting and welding underwater
Underwater Cutting and Welding manual
For diver who want to take a step to be Diving Supervisor read this IMCA Diving supervior manual.
IMCA Air Dive Supervisor Manual
Basic of diving, a must have for all kind of diver whether you are a sport scuba diving or a hard hat commercial diving this US Navy Diving manual will help you with complete guide with depth table for decompression.
US NAVY Diving manual Rev.6 April 2008
For Commercial diver that need handbook for cutting and welding underwater
Underwater Cutting and Welding manual
For diver who want to take a step to be Diving Supervisor read this IMCA Diving supervior manual.
IMCA Air Dive Supervisor Manual