For manual depth calculations by divers, the standard gravity is
often approximated as 10.0 (e.g. 1 bar corresponds to 10 meter), but
libdivecomputer prefers to use the exact value of 9.80665 m/s².
For the McLean Extreme, it has been confirmed that the device also uses
the correct standard gravity internally for the conversion of the sample
depth.
Prefer SI units for internal constants (e.g. density) and calculations.
This results in more consistent conversion formulas across the different
backends.
For the Uwatec backend, this changes makes it also much more visible
that the unit for the depth is either 1 millibar (maximum depth) or 2
millibar (sample depth).
The difference between two unsigned integers can be negative. To avoid
ending up with some very large positive values, an explicit cast to a
signed integer is required.
Depths are normally expected to be always positive, but near the surface
the pressure will be very close to the atmospheric pressure. Therefore
small negative values are not unusual.
The McLean Extreme records a sample every 10 seconds instead of every 20
seconds. This resulted in dive durations that were twice as long as
expected.
Reported-by: David Carron <david_de_carron@hotmail.com>
