SDI Scuba Certification
SDI Scuba Certification Exam Study
Guide 2025 GRADED A+
Define SCUBA - Correct Ans-S - self
C - contained
U - underwater
B - breathing
A - apparatus
List 3 important scuba diving changes that occurred in 1950s - Correct Ans-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 - Correct Ans-1) dive
tables
2) J-valves
3) depth gauges
What sets SDI apart from other training agencies? - Correct Ans-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? - Correct Ans-
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? - Correct Ans-4
times faster because water is about 800 times denser than air.
What is the first color to be absorbed underwater? - Correct Ans-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. - Correct Ans-
Slack tide
If you are caught in a rip current, first swim _____ to the current to get out of it before
swimming towards shore. - Correct Ans-Parallel
Waves are usually caused by - Correct Ans-Wind pushing water on the surface
1|Page
, SDI Scuba Certification
T or F: Anticipate surge action to avoid contact with stationary objects - Correct Ans-
True
What type of marine life cause most diving injuries? - Correct Ans-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? - Correct Ans-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? - Correct Ans-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)? - Correct Ans-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? - Correct Ans-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? - Correct Ans-4x
If a scuba cylinder lasts two hours at sea level, how long will it last at 20 m/66 ft? -
Correct Ans-40 minutes
120 min x 1/3 (vol) = 40 min
How often should a scuba diver equalize during descent? - Correct Ans-At the surface
before descent and every couple of feet
What should you do if you experience discomfort in your ears upon descending? -
Correct Ans-Stop, ascend a few feet until you no longer feel discomfort, equalize again,
then continue with descent
What is a reverse block? - Correct Ans-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? - Correct Ans-
Stop, descend a few feet until pain subsides, wait to allow air to vent, then continue with
ascent
2|Page
SDI Scuba Certification Exam Study
Guide 2025 GRADED A+
Define SCUBA - Correct Ans-S - self
C - contained
U - underwater
B - breathing
A - apparatus
List 3 important scuba diving changes that occurred in 1950s - Correct Ans-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 - Correct Ans-1) dive
tables
2) J-valves
3) depth gauges
What sets SDI apart from other training agencies? - Correct Ans-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? - Correct Ans-
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? - Correct Ans-4
times faster because water is about 800 times denser than air.
What is the first color to be absorbed underwater? - Correct Ans-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. - Correct Ans-
Slack tide
If you are caught in a rip current, first swim _____ to the current to get out of it before
swimming towards shore. - Correct Ans-Parallel
Waves are usually caused by - Correct Ans-Wind pushing water on the surface
1|Page
, SDI Scuba Certification
T or F: Anticipate surge action to avoid contact with stationary objects - Correct Ans-
True
What type of marine life cause most diving injuries? - Correct Ans-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? - Correct Ans-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? - Correct Ans-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)? - Correct Ans-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? - Correct Ans-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? - Correct Ans-4x
If a scuba cylinder lasts two hours at sea level, how long will it last at 20 m/66 ft? -
Correct Ans-40 minutes
120 min x 1/3 (vol) = 40 min
How often should a scuba diver equalize during descent? - Correct Ans-At the surface
before descent and every couple of feet
What should you do if you experience discomfort in your ears upon descending? -
Correct Ans-Stop, ascend a few feet until you no longer feel discomfort, equalize again,
then continue with descent
What is a reverse block? - Correct Ans-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? - Correct Ans-
Stop, descend a few feet until pain subsides, wait to allow air to vent, then continue with
ascent
2|Page
