SDI SCUBA CERTIFICATION EXAM STUDY
GUIDE 2026/2027 – COMPLETE
QUESTIONS WITH 100% VERIFIED
CORRECT ANSWERS.
◎ List 3 important scuba diving changes that occurred in 1950s. ANSWER:- 1)
published USN dive tables
2) invented the personal dive computer
3) equipment manufacturers made improvements to the design and workmanship of
gear
◎ Name 3 different devices that modern dive computers replace. ANSWER:- 1) dive
tables
2) J-valves
3) depth gauges
◎ What sets SDI apart from other training agencies?. ANSWER:- First dive training
agency to provide entry level scuba instruction that incorporates the use of personal
dive computers --> more streamlined scuba course w/ more instruction time in the water
◎ How much larger and closer do objects appear underwater and why?. ANSWER:-
Objects underwater appear 25% larger and 25% closer
As light travels through the airspace created by the mask, it bends, creating a
magnifying effect.
◎ How much faster does sound move through water than air and why?. ANSWER:- 4
times faster because water is about 800 times denser than air.
◎ What is the first color to be absorbed underwater?. ANSWER:- Red (within first 25
feet)
◎ When diving from shore, the best time to dive is when there is the least amount of
tidal current. _______ tide is when there is no horizontal water movement.. ANSWER:-
Slack tide
◎ If you are caught in a rip current, first swim _____ to the current to get out of it before
swimming towards shore.. ANSWER:- Parallel
◎ Waves are usually caused by. ANSWER:- Wind pushing water on the surface
, ◎ T or F: Anticipate surge action to avoid contact with stationary objects. ANSWER:-
True
◎ What type of marine life cause most diving injuries?. ANSWER:- Most diving injuries
result from animal's defensive response to a perceived threat
◎ What should you do if you see a potentially dangerous animal underwater and it does
not leave the area?. ANSWER:- Remain still and calm. Slowly leave area if necessary.
◎ List three different reasons that it is advisable to check with your local dive center
before conducting a dive in an area you are unfamiliar with?. ANSWER:- 1) tidal
conditions
2) marine life
3) first aid for potential injuries in area
◎ What is the absolute pressure (in atm/bar) at 20 meters (66 feet)?. ANSWER:- 3
atm/bar
◎ What will be the volume in a ball that is filled with 2 cubic feet/liters of air at 30
meters (90 feet) when it is taken to surface?. ANSWER:- 8 cubic feet/liter (4x the
volume)
◎ How many more times dense is the air in a ballon at 4 atm/bar compared to air
density at surface?. ANSWER:- 4x
◎ If a scuba cylinder lasts two hours at sea level, how long will it last at 20 m/66 ft?.
ANSWER:- 40 minutes
120 min x 1/3 (vol) = 40 min
◎ How often should a scuba diver equalize during descent?. ANSWER:- At the surface
before descent and every couple of feet
◎ What should you do if you experience discomfort in your ears upon descending?.
ANSWER:- Stop, ascend a few feet until you no longer feel discomfort, equalize again,
then continue with descent
◎ What is a reverse block?. ANSWER:- When air cannot escape freely from an air
space during ascent
causes pain and discomfort in the ears and sinuses
◎ What should you do if you experience a reverse block upon ascending?. ANSWER:-
Stop, descend a few feet until pain subsides, wait to allow air to vent, then continue with
ascent
GUIDE 2026/2027 – COMPLETE
QUESTIONS WITH 100% VERIFIED
CORRECT ANSWERS.
◎ List 3 important scuba diving changes that occurred in 1950s. ANSWER:- 1)
published USN dive tables
2) invented the personal dive computer
3) equipment manufacturers made improvements to the design and workmanship of
gear
◎ Name 3 different devices that modern dive computers replace. ANSWER:- 1) dive
tables
2) J-valves
3) depth gauges
◎ What sets SDI apart from other training agencies?. ANSWER:- First dive training
agency to provide entry level scuba instruction that incorporates the use of personal
dive computers --> more streamlined scuba course w/ more instruction time in the water
◎ How much larger and closer do objects appear underwater and why?. ANSWER:-
Objects underwater appear 25% larger and 25% closer
As light travels through the airspace created by the mask, it bends, creating a
magnifying effect.
◎ How much faster does sound move through water than air and why?. ANSWER:- 4
times faster because water is about 800 times denser than air.
◎ What is the first color to be absorbed underwater?. ANSWER:- Red (within first 25
feet)
◎ When diving from shore, the best time to dive is when there is the least amount of
tidal current. _______ tide is when there is no horizontal water movement.. ANSWER:-
Slack tide
◎ If you are caught in a rip current, first swim _____ to the current to get out of it before
swimming towards shore.. ANSWER:- Parallel
◎ Waves are usually caused by. ANSWER:- Wind pushing water on the surface
, ◎ T or F: Anticipate surge action to avoid contact with stationary objects. ANSWER:-
True
◎ What type of marine life cause most diving injuries?. ANSWER:- Most diving injuries
result from animal's defensive response to a perceived threat
◎ What should you do if you see a potentially dangerous animal underwater and it does
not leave the area?. ANSWER:- Remain still and calm. Slowly leave area if necessary.
◎ List three different reasons that it is advisable to check with your local dive center
before conducting a dive in an area you are unfamiliar with?. ANSWER:- 1) tidal
conditions
2) marine life
3) first aid for potential injuries in area
◎ What is the absolute pressure (in atm/bar) at 20 meters (66 feet)?. ANSWER:- 3
atm/bar
◎ What will be the volume in a ball that is filled with 2 cubic feet/liters of air at 30
meters (90 feet) when it is taken to surface?. ANSWER:- 8 cubic feet/liter (4x the
volume)
◎ How many more times dense is the air in a ballon at 4 atm/bar compared to air
density at surface?. ANSWER:- 4x
◎ If a scuba cylinder lasts two hours at sea level, how long will it last at 20 m/66 ft?.
ANSWER:- 40 minutes
120 min x 1/3 (vol) = 40 min
◎ How often should a scuba diver equalize during descent?. ANSWER:- At the surface
before descent and every couple of feet
◎ What should you do if you experience discomfort in your ears upon descending?.
ANSWER:- Stop, ascend a few feet until you no longer feel discomfort, equalize again,
then continue with descent
◎ What is a reverse block?. ANSWER:- When air cannot escape freely from an air
space during ascent
causes pain and discomfort in the ears and sinuses
◎ What should you do if you experience a reverse block upon ascending?. ANSWER:-
Stop, descend a few feet until pain subsides, wait to allow air to vent, then continue with
ascent
