| Acronym | Meaning |
 | IDC | Instructor Development Course (PADI) |
 | ADT | Actual Dive Time |
 | SSI | Scuba Schools International; Diving Instruction Organization. |
 | MDT | Maximum Dive Time |
 | OW | Open Water Certification; First Certification Level. |
 | NITROX | Any Gas Mixture Of Nitrogen And Oxygen; Though Most Commonly Used For Oxygen Mixtures Above The Normal 21 Per Cent. |
 | MCS | Marine Conservation Society |
 | RD | Rescue Diver (PADI) |
 | HPNS | High Pressure Nervous Syndrome |
 | PADI | Professional Association Of Diving Instructors |