Instruction Manual

9
more information about diving with more than
one gas or for dives with trimix.
With BR-SP from PRE-DIVE you have direct
access to the last used gas setting menu.
2.2. ALGORITHM
Sirius employs the unmodified Bühlmann
ZH-L16C algorithm with gradient factors.
Gradient factors are used to lower the
maximum tolerated inert gas pressure in the
tissues with respect to Bühlmann’s original
values. This results in less nitrogen in the body
at the end of the dive, which under normal
circumstances makes the dive safer. Gradient
factors are expressed in pairs: the first value,
also called GF low, represents the reduction of
the original Bühlmann value that defines the
beginning of the final ascent (relevant only in
decompression dives); the second value, also
called GF high, represents the reduction of
the original Bühlmann value that defines the
residual nitrogen at the surface at the end of
a dive. As an example GF 50/85 will get you to
the surface with a 15% lower gradient factor
with respect to Bühlmann’s original maximum
tolerated inert gas pressure and, if this was a
decompression dive, your first decompression
stop would have been at a depth such that you
would not have exceeded 50% of the gradient
with respect to Bühlmann’s original value at
that depth.
For more information about
gradient factors, please refer to
www.mares.com/sports/diving/gradientfactor
TR-SP from PRE-DIVE displays a table listing
all settings (Fig. 11). From here, TR-LP gives
you direct access to the ALGORITHM menu.
2.2.1. MAIN GF
This is where you set the conservatism level
of the ZH-L16C algorithm via gradient factors.
We use Bühlmann’s original values reduced by
15% as a starting point, and you can make the
algorithm more conservative from there. There
are four predefined sets of gradient factors
with increasing conservatism from R0 (85/85)
to R3 (50/60) for recreational dives and from
T0 (30/85) to T3 (25/40) for tech dives. You
can also enter the GF low and GF high values
directly via the CUSTOM setting. The default
value is R0 (85/85).
2.2.2. PERSONALIZATION
This menu allows you to define additional
conservatism in a way similar to going from
R0 to R1, R2 or R3 but in a more personal
way. It has three submenus, called PHYSIO,
DIVE, I TODAY. The values set in each menu
are subtracted from the MAIN GF values
yielding the values used by Sirius for the
decompression calculations.
PHYSIO allows you to define an additional
conservatism based on how you feel about
yourself and diving overall. Each step from
LOW to MEDIUM to HIGH incrementally
reduces both gradient factor values by 10.
There is also a setting called ADVANCED
(ADV), which increases the gradient factor by
5 so that a maximum of 90/90 can be achieved.
This is only for experienced divers who have
accumulated enough experience to know they
can tolerate such levels of inert gas. We do not
recommend doing this since it increases the
risk of decompression sickness thus Sirius
requires that you insert a code (1234) to allow
the setting.
The value set in PHYSIO remains stored until
you manually change it. The default value is
OFF.
DIVE allows you to define an additional
conservatism based on how you feel about
the dive conditions. Each step from LOW to
MEDIUM to HIGH incrementally reduces both
gradient factor values by 3. If you think there
will be much current or the water will be
very cold, pick one of these settings. Since
conditions can actually be different from what
you expected, this parameter can be edited
also DURING the dive (via the underwater
menu). The default value is OFF.
The value set in DIVE resets automatically to
OFF at midnight.
I TODAY allows you to define an additional
conservatism based on how you feel about
yourself today, for instance to account for
a restless night or not having hydrated
sufficiently. Each step from LOW to MEDIUM
to HIGH incrementally reduces both gradient
factor values by 5.
The default value is OFF. Also the value set
in I TODAY resets automatically to OFF at
midnight.
2.2.3. REPETITIVE DIVES
The original Bühlmann algorithm assumes
normal offgassing of inert gas via diffusion
after a dive. This seems to work well for
most people and indeed most dive computers
available today compute repetitive dives like
this. There is evidence however that some
people produce bubbles after a dive, or
produce more bubbles than others, and these
bubbles though harmless slow down the
offgassing process. Surface intervals of three
hours or longer are known to dissipate most
if not all bubbles. Sirius allows you to account
for this by applying an additional conservatism
to repetitive dives, reducing both gradient
factor values by 8 upon surfacing from a dive
and then increasing it again by 1 every 15
minutes of surface interval. When setting REP
DIVE to ON you will have recovered the full
gradient factor values after a two-hour surface
interval. Any dive started before such surface
interval will carry an automatic additional
gradient factor reduction. If you set the value
to OFF, the GF values are not modified during
a surface interval.
2.2.4. MULTIDAY
Increasing inert gas load on your tissues over
several days of diving has effects that are not
fully understood and are different from person
to person. Most dive computers available today
do not account for this and compute simple
inert gas offgassing by diffusion. Sirius allows
you to increase the conservatism automatically
for each day of diving with less than 24-hours
of surface interval by reducing both gradient
factor values by 2 on the second day, an
additional 2 on the third day and an additional
2 on the fourth day up to a maximum of 6.
2.3. GAS INTEGRATION
This menu contains five submenus. The first
one allows you to pair the tank modules to
Sirius. Please refer to section 1.6 for the
description of the pairing process.
The second menu, TANK VOLUME, allows
you to set the size of the volume of the tank,
individually for G1 through G5. This parameter
is important for a correct evaluation of your
gas consumption in l/min or cu ft /min. Default
setting is 12l for metric system and 80 cubic
feet in imperial. For the imperial setting it
is paramount that you also set the correct
operating tank pressure, since the size of the
tank is referenced to this pressure.
The third menu, MAX PRESSURE, is where
you define the nominal fill pressure of your
tanks. This can be set individually for each
tank (G1 through G5). This value is used to
scale the graphic tank representation but also
to define the pressure ranges for color coding
(described in section 2.3.1). When the units are
set to ft/°F/psi, this value is important because
together with the tank volume it allows Sirius
to correctly evaluate your gas consumption
in cu ft/min. Default values are 200bar and
3000psi.
The fourth menu, HALF TANK, is the value
at which Sirius triggers a half tank warning.
This can be set individually for each tank (G1
through G5). This value is also used in the
definition of the pressure ranges for color
coding as described below. Default values are
100bar and 1500 psi.
The fifth menu, TANK RESERVE, is the value
at which an alarm is triggered because
you should always be at the surface before
reaching this level. Furthermore, this value is
used to calculate the TTR value (see section
8.3.5 and 9.1). This can be set individually for
each tank (G1 through G5). Default values are
50bar and 500psi.
2.3.1. COLOR CODING FOR PRESSURE
RANGES
In addition to a numeric value for the tank
pressure, Sirius uses color coding for an
immediate at-a-glance tank pressure
visualization. The color is applied to the lower
screen divider. The pressure range from
operating tank pressure to empty tank is
split into 4 ranges, from BLUE to GREEN to
YELLOW to RED. The ranges are so defined:
BLUE: the upper half between MAX PRESSURE
and HALF TANK
GREEN: lower half between MAX PRESSURE
and HALF TANK
YELLOW: between HALF TANK and
50bar/500psi.
RED: below 50bar / 500psi
2.4. WARNINGS
2.4.1. MAX DEPTH
Sirius allows you to set an alarm at a depth
independent of the MOD. The default value
is OFF. Using TR-SP or BR-SP you can set it
between 10m / 30ft and up to just shy of the
MOD, in 1m / 5ft increments. Upon reaching
the defined depth an alarm similar in behaviour