Shearwater Tern User manual

Operating Instructions

Page 2 Doc. 15301-RevB (2023-11-24)

Table of Contents

Table of Contents�� 2

Conventions Used in this Manual�� 4

1� Introduction�� 5

1�1� Notes on this manual�� 6

1�2� Modes Covered by this Manual�� 6

2� Basic Operation �� 7

2�1� Turning On ��7

2�2� Buttons�� 8

2�3� Changing between Modes�� 9

2�4� Owner Information Screen �� 9

2�5� Function Button�� 9

3� Dive Mode Interface �� 10

3�1� Default Dive Setup��10

3�2� Dive Mode Differentiation��10

3�3� Main Screen Layout�� 11

3�4� Detailed Descriptions �� 12

3�5� Info Screens��16

3�6� Info Screen Descriptions �� 17

3�7� Home Screen Customization �� 21

3�8� Alerts�� 23

4� Safety and Decompression Stops��25

4�1� Safety Stops�� 25

4�2� Decompression Stops ��26

5� Decompression and Gradient Factors ��27

5�1� Decompression Information Accuracy �� 28

6� Example Dives��29

6�1� AIR mode Example Dive ��29

6�2� 3 GasNx mode Example��30

6�3� Gauge Mode�� 32

7� Freedive Mode��33

7�1� Default Freediving Layout��33

7�2� Freediving Info Screens��34

7�3� Freediving Sets ��34

8� Dive Tools��36

8�1� Tag Log ��36

8�2� Reset Average Depth��36

8�3� Test Alerts �� 37

8�4� Deco Planner�� 37

8�5� NDL Planner ��39

9� Watch Mode �� 40

9�1� Date And Time �� 40

9�2� Watch Tools�� 40

9�3� Watch Face Colors ��42

10� Menus�� 43

10�1� Main Menu��43

11� Settings Reference �� 49

11�1� Dive Settings Menu��49

11�2� Deco Menu��54

11�3� Gas / Gases ��55

11�4� Display��56

11�5� Watch��58

11�6� General��59

12� Firmware Update and Log Download�� 60

12�1� Shearwater Cloud Desktop �� 60

12�2� Shearwater Cloud Mobile��62

13� Tern Strap��63

14� Charging ��63

15� Troubleshooting��65

15�1� Warnings and Information Displays��65

16� Storage and Maintenance ��67

16�1� AMOLED Burn In ��67

17� Servicing��67

18� Glossary ��67

19� Tern Specifications ��68

20� Regulatory Information�� 69

21� Contact�� 70

Operating Instructions

Page 3 Doc. 15301-RevB (2023-11-24)

Conventions Used in this Manual

These conventions are used to highlight important

information:

INFORMATION

Information boxes contain useful tips

for getting the most out of your Tern�

CAUTION

Caution boxes contain important

instructions on operating the Tern�

WARNING

Warning boxes contain critical

information that may affect your

personal safety�

This computer has bugs. Although we haven’t found them all yet,

they are there. It is certain that there are things that this computer

does that either we didn’t think about, or planned for it to do

something different. Never risk your life on only one source of

information. Use a second computer or tables. If you choose to

make riskier dives, obtain the proper training and work up to them

slowly to gain experience.

This computer will fail. It is not whether it will fail but when it will

fail. Do not depend on it. Always have a plan for how to handle

failures. Automatic systems are no substitute for knowledge and

training.

No technology will keep you alive. Knowledge, skill, and practiced

procedures are your best defense (except for not doing the dive, of

course).

WARNING

This computer is capable of calculating deco stop requirements. These

calculations are at best a guess of real physiological decompression

requirements. Dives requiring staged decompression are substantially

more risky than dives that stay well within no-stop limits.

Diving with rebreathers and/or diving mixed gases and/or performing

staged decompression dives and/or diving in overhead environments

greatly increases the risk associated with scuba diving.

YOU REALLY ARE RISKING YOUR LIFE

WITH THIS ACTIVITY.

DANGER

Operating Instructions

Page 4 Doc. 15301-RevB (2023-11-24)

Features

• Vivid full color 1�3” AMOLED display

• Stainless steel bezel�

• Crush proof to 120m / 390ft

• Air, Single-gas Nitrox, and multi-gas Nitrox modes

• Up to 3 customizable gases up to 100% oxygen

• Simplified recreational diving modes

• 2 customizable layouts for every dive mode

• Bühlmann ZHL-16C with gradient factors

• Full decompression support

• No lockout for violating no-decompression limit

• No lockout for violating deco stops

• Quick NDL and full decompression planner built in

• CNS Tracking

• Gas density tracking

• Dedicated Freedive Mode

• Customizable vibration alerts

• Programmable depth sampling

• 3 watch faces available in 15 colors

• Bluetooth Dive log uploading to Shearwater Cloud

• Free firmware updates

1. Introduction

The Shearwater Tern is a dive computer for beginner to

expert divers�

Please take the time to read this manual� Your safety

may depend on your ability to read and understand the

Tern displays�

Diving involves risk and education is your best tool for

managing this risk�

Do not use this manual as a substitute for proper dive

training and never dive beyond your training� What you

don’t know can hurt you�

Operating Instructions

Page 5 Doc. 15301-RevB (2023-11-24)

1.2. Modes Covered by this Manual

This manual provides operating instructions for the Tern in Watch

Mode as well as ve Dive Modes:

• Air

• Nitrox

• 3 GasNx

• Gauge

• Freedive

Some features of the Tern only apply to certain dive modes. Look

for the corresponding mode icons throughout the manual to help

distinguish which features are available in the various modes.

If not otherwise indicated, features described are applicable in all

dive modes.

Change the Dive Mode from the Dive Settings menu�

See details on page 48�

1.1. Notes on this manual

This manual contains cross-references between

sections to make it easier to navigate�

Underlined text indicates the presence of a link to

another section�

Do not change any settings on your Tern without

understanding the consequence of the change. If

you are unsure, consult the appropriate section of the

manual for reference�

This manual is not a substitute for proper training�

OC

BO

CC

FD

OC

BO

CC

FD

GA

OC

3Nx

OC

AIR

Firmware Version: V25

This manual corresponds to firmware version

V25�

Feature changes may have been made since this

release and might not be documented here�

Check the release notes on Shearwater.com for a

complete list of changes since the last release.

Nx

Operating Instructions

Page 6 Doc. 15301-RevB (2023-11-24)

2. Basic Operation

2.1. Turning On

To turn the Tern On, press any button�

Auto-on

The Tern will automatically turn-on and enter dive

mode when submerged underwater� This is based on

pressure increase and not on the presence of water�

When auto-on is activated, the Tern will enter the last

configured dive mode�

Auto-on Details

The Tern automatically powers on and enters dive

mode when the absolute pressure is greater than 1100

millibar (mbar)�

For reference, normal sea level pressure is 1013 mbar

and 1 mbar of pressure corresponds to approximately

1 cm (0�4”) of water� So, when at sea level, the Tern

will automatically power on and enter dive mode

when about 0�9 m (3 ft) underwater�

If at higher altitude, automatic power on will occur at

a deeper depth� For example, when at 2000 m (6500

ft) altitude the atmospheric pressure is only about

800 mbar� Therefore, at this altitude the Tern must

be submerged underwater by 300 mbar to reach an

absolute pressure of 1100 mbar� This means the auto-

on occurs at about 3 m (10 ft) underwater when at an

altitude of 2000 m�

Do Not Rely On The Auto-On Feature

This feature is supplied as a backup for

when you forget to turn on your Tern or

forget to place it in dive mode�

Shearwater recommends turning your

computer on manually and entering dive

mode before each dive to confirm proper

operation and to double check battery

status and setup�

Operating Instructions

Page 7 Doc. 15301-RevB (2023-11-24)

2.2. Buttons

All Tern operations are simple single button presses�

No need to remember all the button rules below�

Button hints make using the Tern easy�

MENU Button (Lower Left)

From the main screen >Brings up the menu

In a menu >Moves down to the next menu item

INFO Button (Lower Right)

From the main screen >Cycles through info screens

In a menu >Exits back to the previous menu or main

screen

LIGHT button (Upper Left)

From the main screen >Cycles brightness levels

In a menu >Moves up to the next menu item

FUNCTION Button (Upper Right)

From the main screen >Configurable shortcut

In a menu >Selects menu item

FUNC

(Upper Right)

LIGHT

(Upper Left)

MENU

(Lower Left)

INFO

(Lower Right)

Button Hints

When in a menu, button hints label each button:

In the example above, the hints tell us:

• Use LIGHT to move up a menu item

• Use MENU to move down a menu item

• Use FUNC to select a menu item

• Use INFO to go back to the home screen

Button Hint Icons:

Dive

Watch Tools

Gases ✘

Gases

UP

DOWN

HOME

CANCEL

SAVE

SELECT

UP

DOWN HOME

Deco Model

ZHL16C+GF

GF Conserv.

High 45/80

Last Stop

3 m

BACK

Operating Instructions

Page 8 Doc. 15301-RevB (2023-11-24)

2.3. Changing between Modes

The two primary modes are Watch Mode and Dive

Mode� Watch Mode is only available at the surface�

Switching to Dive Mode

To change from Watch

Mode to Dive Mode

manually, press the

Menu button and select

Dive from the main

menu�

Dive Mode will

automatically be

triggered when a dive

starts�

Changing dive modes is covered on page 48�

Switching to Watch Mode

To change from Dive

Mode to Watch Mode,

press the Menu button

and select Watch from

the main menu�

By default, the Tern will

not automatically revert

back to Watch Mode�

This behavior can be

modified in the display

Timeouts menu� See

page 56�

Dive

Watch Tools

2.4. Owner Information Screen

Upon entering Dive

Mode, the owner

information screen

will be displayed for 15

seconds or until any

button is pressed�

Owner and contact

information can be

changed in the User

Info menu (page 58)�

This display also confirms the current alert notification

settings and tests the alerts� Alert notification settings

can be changed in the top-level Alerts menu (page

51)�

2.5. Function Button

The function (upper

right) button is a

customizable shortcut

that makes accessing

your most used

functions on the Tern a

little easier�

The function button

can be customized

independently for every

mode of operation�

For Watch Mode, the function button can be

customized in Settings > Watch�

For each dive mode, the function button can be

customized in Settings > Dive�

P

S

I

DECO

20 2 14

T1

1850

O2/He

21/00

ft min

TTS

.0

0

ft

mh

342

SURFACE

OC

21

%

mh

342

SURFACE

NDL TTS

----

FD

OC

Watch

Select Gas

Dive Tools

Owner:SCUBA Sammie

Contact:555-123-4567

Vib: ON

Edit in Settings\Gen

Operating Instructions

Page 9 Doc. 15301-RevB (2023-11-24)

3. Dive Mode Interface

3.1. Default Dive Setup

The Tern comes pre-configured for recreational diving�

The default dive mode for the Tern is a simple Air only

mode�

As a quick reference, a diagram of the default diving

display is shown below�

Many attributes of this default mode are shared with

the other dive modes� The following sections go into

detail about each screen element�

See the AIR mode Example Dive on page 28 for a

walk through of how this screen changes through all

phases of a dive�

42

:

18

.0

18

m

21

%

NDL MAX

m

33.5

15

6

AIR

!

Battery Indicator

Depth

Dive Mode Ascent Rate

No Deco

Limit

Maximum

Depth

Alert

Indicator

Dive Time

Active Gas

AIR mode with Big screen

layout

3.2. Dive Mode Differentiation

Each dive mode is designed to best suit a particular

type of diving�

Air

Designed for use during recreational, air only,

no-decompression diving activities�

• Simple Set-up

• Air (21% oxygen) only

• No gas switching underwater

Nitrox (Single Gas)

Designed for use during recreational, Nitrox,

no-decompression diving activities�

• Single Gas Nitrox up to 40% oxygen

• No gas switching underwater

3 GasNx (Three Gas Mode)

Designed for use during advanced diving activities

including light technical diving involving planned

decompression�

• Three programmable gases

• Support for gas switching

• Nitrox up to 100%

• Edit gas mixes underwater

Gauge

Gauge Mode is a simple depth and time display (a�k�a�

a bottom timer)� See page 31�

• No tissue tracking

• No decompression information

Freedive

Optimized for use while freediving� See page 32�

• Freediving sets�

Change the Dive Mode from the Dive Settings menu�

See details on page 48�

Operating Instructions

Page 10 Doc. 15301-RevB (2023-11-24)

Standard layout

The Standard screen layout has four rows and

provides the most information on the screen, though

with a smaller font size�

The Top, Bottom, and Deco row content are reserved

for the most critical information and are fixed, while

pressing the INFO button scrolls through additional

data in the Info row�

In the Standard screen layout, the right Deco row

slot displays maximum depth by default but can be

customized�

The Info row can also be customized with up to three

pieces of information� Read more about Home Screen

Customization on page 20�

3.3. Main Screen Layout

The Tern has two different screen layouts available in

every dive mode, Big and Standard�

Change the Screen layout from the Dive Settings Menu�

See details on page 48�

Big layout

42

:

18

.0

24

m

21

%

NDL MAX

m

31.6

12

6

Top Row

Depth, Mode

& Ascent Rate

Info Row

NDL,

Deco Info

Bottom Row

Dive Time

m

38.6

23 19

:

DECO

6 2

SurfGF

127

m min

MAX

m

38.7

O2

21

% %

6

!

Top Row

Depth, Mode

& Ascent Rate

Deco Row

NDL,

Deco Info

Info Row

Customizable

Bottom Row

Dive Time

The Big screen layout provides the largest font size at

the expense of on screen information�

The top and bottom row contents are reserved for the

most critical information and are fixed, while pressing

the INFO button scrolls through additional data in the

Info row�

In the Big screen layout, the right Info row slot

displays maximum depth by default but can be

customized� Read more about Home Screen

Customization on page 20�

The Big screen layout is the default layout for all dive

modes�

Operating Instructions

Page 11 Doc. 15301-RevB (2023-11-24)

3.4. Detailed Descriptions

The Top Row

The top row shows depth, ascent rate, battery and

mode information�

Depth

Displayed to one decimal place in feet or meters�

Note: If the depth shows a Flashing Red zero or shows a

depth at the surface, then the depth sensor needs service�

Ascent Rate Display

Shows how fast you are currently ascending

graphically and numerically�

1 arrow per 3 meters per minute (mpm) or 10 feet per

minute (fpm) of ascent rate�

Note: Deco calculations assume 10mpm (33fpm)

ascent rate�

6

ft

125

.

7

m

32.

12

20

6

WHITE when less than 9 mpm / 30 fpm (1

to 3 arrows)

YELLOW when greater than 9 mpm /

30 fpm and less than 18 mpm / 60 fpm

(4 or 5 arrows)

FLASHING RED when greater than

18 mpm / 60 fpm (6 arrows)

Freedive Mode Ascent / Descent Rate Display

Freedivers ascend much faster than SCUBA divers� So,

ascent rate in Freedive Mode is measured in feet per

second (fps) or meters per second (mps) rather than

feet per minute or meters per minute�

In Freedive Mode, 1 arrow per 1 fps / 0�3 mps�

Descent rate is displayed in addition to ascent

rate in Freedive Mode�

Read more about Freedive Mode on page 32�

Battery Icon

The battery icon is shown on the surface but

disappears when diving� If low or critical then the

battery icon will appear while diving�

Dive Mode Indicator

The dive mode indicator is only shown at the surface�

WHITE when battery charge is OK

YELLOW when battery needs to

be charged�

RED when battery must be

charged immediately�

OC

3Nx

OC

BO

CC

FD

OC

BO

CC

FD

GA

OC

AIR

Nx

Air

Nitrox (Single Gas)

3 GasNx (Three Gas Mode)

Freedive Mode

Gauge Mode

m

26

.1

TTS

6

NDL

AIR

OC

BO

CC

FD

0.9

0.4

Operating Instructions

Page 12 Doc. 15301-RevB (2023-11-24)

Safety Stop Counter

The safety stop counter replaces NDL

and counts down automatically when

the diver ascends into safety stop range�

The counter will display “CLEAR” when

the safety stop has been completed�

Safety stops may be turned off, set to

fixed times of 3, 4, or 5 minutes, set to

adapt based on dive conditions, or be

set to count up from zero�

Count-up

When decompression diving, the

safety stop will begin once all

decompression obligation has been

cleared�

See the Safety Stops section on page

24 for details�

Maximum Depth

The maximum depth of the current

dive� When not diving, displays the

maximum depth of the last dive�

The right deco row box can be customized in every

dive mode� See Home Screen Customization on page

20 for details�

The Deco Row

The Deco Row is only shown in the Standard layout,

however, the Deco row information described in this

section is shown on the first page of the info row in

the Big layout�

No Decompression Limit (NDL)

Deco Stop Depth and Time

Once Mandatory decompression is required, NDL will

be replaced by decompression information�

By default the Tern uses a 3m (10ft) last deco stop

depth� When in decompression, you may perform

your last deco stop deeper if you wish - deco

calculations will remain accurate� If you choose to do

this, depending on your breathing gas, the predicted

time-to-surface may be shorter than the actual TTS

since off-gassing may occur slower than the algorithm

expects� There is also an option to set the last stop to

6m (20ft)� This does not affect no-deco safety stops�

See the Decompression Stops section on page 25

for details�

The time remaining, in minutes, at the

current depth until decompression stops

will be necessary�

Displays in Yellow when the NDL is less

than or equal to 5 minutes�

125

6 2

O2/He

m min

DECO

The shallowest depth to which you

can ascend and how long to hold

that stop�

42

0

CLEAR

1:14

42

0

SAFETY

3:22

125

O2/He

m

38.7

MAX

23

NDL

21

125

O2/He

m

38.7

MAX

23

NDL

21

.0

0

ft

STOPWATCH

SURFACE

Deep

19:16

FD

CLEAR

SAFETY

Important!

All decompression information including

Deco Stops, NDL, and Time to surface are

predictions that assume:

• Ascent rate of 10mpm / 33fpm

• Decompression stops will be followed

• All programmed gases will be used as

appropriate

Read more about PPO2 Limits on page

52�

O2

21

%

58

27 1

mmin

PPO2

.21

19 22

:

O2

21

%

58

27 1

mmin

PPO2

.21

19 22

:

ft

125

.6

MODCNS

%

11

mmin

PPO2

1.0257

TTS

OC

SURFACE

mh

3412

NDL

MODCNS

%

11

mmin

PPO2

1.71271

SURFACE

42

:

18

.0

60

ft

21

%

NDL MAX

m

31.6

15

22

OC Rec

!

Default Info row in Big layout

Pressing the info (bottom right) button will scroll

through info screens and show additional information

during a dive� See the Info Screens section on page

15 for details�

Operating Instructions

Page 14 Doc. 15301-RevB (2023-11-24)

Alert Indicator

Indicates there is a persistent warning

condition�

When the computer detects a dangerous situation,

such as high PPO2, a warning is triggered� The large

primary warning can be dismissed, but for some

situations this alert icon will persist until the condition

that caused the warning is resolved� See the Alerts

section on page 22 for more information�

The Bottom Row

Dive Time

The current length of the dive in minutes

and seconds

Surface Interval

When on the surface, the Dive Time is

replaced by a surface interval display�

Shows the minutes and seconds since the end of your

last dive�

Above one hour, the surface interval is displayed in

hours and minutes� Above 4 days, the surface interval

is displayed in days�

42 18

:

185021/00

42

:

18

ft

103.6 4:57

21

%

!

1753 20450

SURFACE

mh

3412

18/45

0.7

Bottom Row, AIR Mode on a dive

Alternate Active Gas Location

When the info row is not displaying the active

breathing gas, this value is displayed in the bottom

row at the very bottom of the computer display�

Notification Setting Icon

Indicates what notifications are turned on� Only

available at the surface�

Vibrate

42

:

18

ft

103.6 4:57

21

%

!

The surface interval resets when

decompression tissues are cleared�

Silent Mode

Operating Instructions

Page 15 Doc. 15301-RevB (2023-11-24)

3.5. Info Screens

Info screens provide more information than is

available on the main screen�

From the main screen, the INFO (bottom right) button

steps through info screens�

When all info screens have been viewed, pressing

INFO again will return to the main screen�

Pressing the MENU (bottom left) button will also

return to the home screen at any time�

Info screens also automatically time-out after 10

seconds, returning to the home screen� This prevents

critical NDL and DECO information from being hidden

for an extended period�

When using the Standard layout, the Tissues Info

screen will not automatically time out�

Note that although these screens are generally

representative of the Tern display, info screen content

varies for each mode� For example, decompression

related info screens are not available in gauge mode�

LAST DIVE

30.7 26:57

m

mmin

SURFACE

MAX AVG

13.7

m

39.4

m

mmin

SURFACE

ft

125.6

MODCNS

%

11

mmin

PPO2

1.0257

TTS

OC

SURFACE

mh

3412

NDL

mmin

GF

35/75

GF99

22

%

15

TTS

SURFACE

mmin

SURFACE

TISSUES

TEMP

21 49

BATTERY

%

�C

mmin

SURFACE

mBar SURF

1013

mBar NOW

4943

mmin

SURFACE

TIME

2:31

EOD

2:46

mmin

SURFACE

10

:

26

.6

31

m

21

%

NDL MAX

m

34.5

10

m

38.8

O2

21

%

DECO

15

9

1

mmin

PPO2

1.02

19 22

:

TTS

m

38.8

O2

21

%

DECODECO

15

9

1

mmin

PPO2

1.01

19 22

:

TTS

Press the INFO button

(bottom right), to step

through Info Screens

Return to Main Screen by:

•Pressing MENU button

•Stepping past last screen

•Waiting 10 Seconds (most screens)

Big layout Info row

location

Standard layout Info

row location

Operating Instructions

Page 16 Doc. 15301-RevB (2023-11-24)

3.6. Info Screen Descriptions

Last Dive Info

Maximum depth and dive time from the last dive� Only

available at the surface�

Maximum Depth

The maximum depth of the current

dive� When not diving, displays the

maximum depth of the last dive

Average Depth

Displays the average depth of the

current dive, updated once per

second� When not diving, displays

the average depth of the last dive�

Maximum Operating Depth

MOD is the maximum allowable

depth of the current breathing gas

in the currently selected depth units

as determined by PPO2 limits�

Displays in Flashing Red when exceeded�

Read more about PPO2 Limits on page 52�

LAST DIVE

30.7 26:57

m

mmin

SURFACE

MAX AVG

13.3

m

31.6

m

mmin

SURFACE

MODCNS

%

11

mmin

PPO2

.2157

SURFACE

MAX AVG

13.3

m

31.6

m

mmin

SURFACE

CNS Toxicity Percentage

Central Nervous System oxygen

toxicity loading percentage� Turns

Red when greater than 100%�

The CNS percentage is calculated

continuously, even when on the

surface and turned off� When deco

tissues are reset, the CNS will also

be reset�

The CNS value (short for Central Nervous System

Oxygen Toxicity) is a measure of how long you have

been exposed to elevated partial pressures of oxygen

(PPO2) as a percentage of a maximum allowable

exposure� As PPO2 goes up, the maximum allowable

exposure time goes down� The table we use is from

the NOAA Diving Manual (Fourth Edition)� The

computer linearly interpolates between these points

and extrapolates beyond them when necessary�

Above a PPO2 of 1�65 ATA, the CNS rate increases at a

fixed rate of 1% every 4 seconds�

During a dive the CNS never decreases� When back at

the surface, a half-life of elimination of 90 minutes is

used�

So for example, if at the end of the dive the CNS was

80%, then 90 minutes later it will be 40%� In 90 more

minutes it will be 20%, etc� Typically after about 6

half-life times (9 hours), everything is back close to

equilibrium (0%)�

ft

125.6

MODCNS

%

11

mmin

PPO2

1.0257

TTS

OC

SURFACE

mh

3412

NDL

MODCNS

%

101

mmin

PPO2

.21271

SURFACE

Operating Instructions

Page 17 Doc. 15301-RevB (2023-11-24)

mmin

GF

35/75

GF99

22

%

136

%

SurfGF

SURFACE

mmin

GF

35/75

GF99

22

%

15

TTS

SURFACE

mmin

GF

35/75

GF99

22

%

15

TTS

SURFACE

Gradient Factor

The deco conservatism value when

the deco model is set to GF� The low

and high gradient factors control

the conservatism of the Bühlmann

GF algorithm� See “Clearing up the

Confusion About Deep Stops” by

Erik Baker for more information�

GF99

The current gradient factor as a

percentage (i�e� super-saturation

percent gradient)

0% means the leading tissue super-saturation is equal

to ambient pressure� Displays “On Gas” when tissue

tension is less than the inspired inert gas pressure�

100% means the leading tissue super-saturation is

equal to the original M-Value limit in the Bühlmann

ZHL-16C model�

GF99 is displayed in Yellow when the current gradient

factor modified M-Value (GF High) is exceeded�

GF99 is displayed in Red when 100% (un-modified

M-Value) is exceeded�

Time-To-Surface (TTS)

The time-to-surface in minutes� This

is the current time to ascend to the

surface including the ascent plus

all required deco stops and safety

stops�

Temperature

The current temperature in degrees

Celsius or degrees Fahrenheit�

Temperature units can be set in the

Display settings menu�

Battery

The Tern’s remaining battery level

expressed as a percentage�

Displays in yellow when battery is low and needs to

be recharged� Displays in red when battery is critically

low and must be recharged immediately�

Pressure

The pressure in millibars� Two values are shown,

the surface (surf) pressure and the current (now)

pressure�

Note that typical pressure at sea level is 1013 millibar,

although it may vary with the weather (barometric

pressure)� For example, in a low pressure system

surface pressure may be as low as 980 millibar, or as

high as 1040 millibar in a high pressure system�

For this reason, the PPO2 displayed on the surface

may not exactly match the FO2 (fraction of O2),

although the displayed PPO2 is still correct�

The surface pressure is set based on the lowest

pressure the Tern sees in the 10 minutes prior to the

start of a dive� Therefore, altitude is automatically

accounted for and no special altitude setting is

required�

TEMP

21 49

BATTERY

%

�C

mmin

SURFACE

TEMP

21 49

BATTERY

%

�C

mmin

SURFACE

mBar SURF

1013

mBar NOW

4943

mmin

SURFACE

Operating Instructions

Page 18 Doc. 15301-RevB (2023-11-24)

Time

In a 12 or 24 hour format� Time

format can be changed in the watch

settings menu�

End of Dive Time (EOD)

This is similar to TTS but is

expressed as a time of day�

The time of day at which you

can expect to surface if you

depart immediately, ascend at

10mpm or 33fpm, change gases

when prompted, and perform all

decompression stops as directed�

TIME

2:31

EOD

2:46

mmin

SURFACE

TIME

2:31

EOD

2:46

mmin

SURFACE

Operating Instructions

Page 19 Doc. 15301-RevB (2023-11-24)

Sample Tissue Bar GraphsTissues Bar Graph

The tissues bar graph shows the tissue compartment

inert gas tissue tensions based on the Bühlmann ZHL-

16C model�

The fastest tissue compartment is shown on the top,

and the slowest on the bottom� Pressure increases to

the right�

The vertical cyan line shows the inert gas inspired

pressure� The yellow line is the ambient pressure� The

red line is the ZHL-16C M-Value pressure�

Tissues that are supersaturated above ambient

pressure are shown in yellow, and tissues that are

supersaturated above the M-Value are shown in red�

Note that the scale for each tissue compartment is

different� The reason the bars are scaled in this way is

so that the tissues tensions can be visualized in terms

of risk (i�e� how close they are as a percentage to

Bühlmann’s original super- saturation limits)� Also, this

scale changes with depth, since the M-Value line also

changes with depth�

mmin

SURFACE

TISSUES

mmin

SURFACE

TISSUES

Inspired inert

gas pressure

Ambient

Pressure

Increasing

Pressure

M-Value

Pressure

16 tissue

compartments

{

mmin

SURFACE

TISSUES

On surface (sat� with air)

Note: Gas is 79% N2 (21% O2, or Air)

mmin

SURFACE

TISSUES

Immediately after descent

Deep Stop

mmin

SURFACE

TISSUES

On Gassing

mmin

SURFACE

TISSUES

Last deco Stop

Note: Gas is now 50% O2and 50% N2

mmin

SURFACE

TISSUES

Operating Instructions

Page 20 Doc. 15301-RevB (2023-11-24)

3.7. Home Screen Customization

In the Standard layout, the Home screen (first page)

Info Row is customizable with 1, 2 or 3 items�

Each Dive Mode’s home screen can be customized

independently�

The right slot of the Info Row in the Big layout, and

the right Deco Row slot in standard mode are also

customizable�

Details about how to customize the Home screen can

be found on page 49�

Home Screen

Reset

AIR

# Values: 2

O2

21

%

PPO2

.21

Back

Home Screen

Reset

3GasNx

# Values: 3

�+5

GF99

22

%

Back

0 136

%

SurfGF

m

0.0

�+5

0

GF99

22

%

136

%

SurfGF

m

38.7

MAX

NDL

--

OC

3Nx

SURFACE

mh

3412

21%

OC

3Nx

Home Screen

Reset

NDL

--

AIR

TEMP

21

�C

Back

ft

0.0

O2

21

%

PPO2

1.01

m

38.7

MAX

NDL

--

AIR

SURFACE

mh

3412

.0

0

ft

21

%

mh

342

SURFACE

NDL

--

TEMP

21

�C

OC

AIR

Home Screen Customization Options

Option Info Display

Current Gas

PPO2

CNS %

MOD

Gas Density

Deco

Consrv

GF99

Ceiling

@+5

Δ+5

Tissues

Surf� GF

TTS

Option Info Display

Time of Day

Date

Stopwatch

End of Dive

t@Max

Depth

Temperature

Battery %

mBar Now

mBar Surf

NDL

Max Depth

Avg� Depth

O2

21

%

58

27 1

mmin

PPO2

.21

19 22

:

ft

125.6

MODCNS

%

11

mmin

PPO2

1.0257

TTS

OC

SURFACE

mh

3412

NDL

ft

125.6

MODCNS

%

11

mmin

PPO2

1.0257

TTS

OC

SURFACE

mh

3412

NDL

MODCNS

%

11

mmin

PPO2

.2157

SURFACE

mmin

GF

35/75

GF99

22

%

136

%

SurfGF

SURFACE

mmin

GF

35/75

GF99

22

%

15

TTS

SURFACE

mmin

Δ+5

+8

@+5

20

CEIL

8

SURFACE

mmin

Δ+5

+8

@+5

20

CEIL

26

SURFACE

m

0.0

T1 �+5

1753

T2

20450

DECO

mmin

TTS

OC Tec

SURFACE

mh

3412

18/45

---- -

mmin

SURFACE

TISSUES

mmin

GF

35/75

GF99

22

%

136

%

SurfGF

SURFACE

125

14

T1

min

TTS

23

20

NDL

MAX AVG

13.3

m

31.6

m

mmin

SURFACE

MAX AVG

13.3

m

31.6

m

mmin

SURFACE

TIME

2:31

EOD

2:46

mmin

SURFACE

TIME

2:31

EOD

2:46

mmin

SURFACE

.0

0

ft

MAX

ft

103.6 4:57

STOPWATCH

SURFACE

Deep

19:16

FD

TEMP

21 49

BATTERY

%

�C

mmin

SURFACE

TEMP

21 49

BATTERY

%

�C

mmin

SURFACE

mBar SURF

1013

mBar NOW

4943

mmin

SURFACE

mBar SURF

1013

mBar NOW

4943

mmin

SURFACE

DATE

MAY-30

EOD

2:43

mmin

SURFACE

t@MAX

12:14

EOD

2:43

mmin

SURFACE

DensityCNS

%

11

mmin

PPO2

.211.3

g/L

SURFACE

Shearwater TERN User manual

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