Shearwater TERN - 2. Basic Operation; Turning On

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�