[PATCH] VPM-B: Calculate first_stop_pressure before starting ascent

[Rick Walsh]

On 22 August 2015 at 14:41, Rick Walsh <rickmwalsh at gmail.com> wrote:

> The Boyle's law compensation depends on first_stop_pressure.  To produce
> profiles similar to other VPM-B implementations, we should calculate it as
> the
> ceiling before starting the ascent.
>
> Commit 159c9eb2c1c19dfbf650f2b0cc28e0ef1f45c964, Compare ceiling to next
> stop
> rather than try to ascent for VPM-B, changed (VPM-B) to consider the
> current
> ceiling rather than an incremental ascent between one stop level and the
> next.
> However, the initial ascent generally steps through several stop levels, so
> first_stop_pressure was still not calculated as the ceiling prior to
> commencing
> the calculated ascent.
>
> Signed-off-by: Rick Walsh <rickmwalsh at gmail.com>
>

To show what this actually does to the calculated profiles, I have made a
new column on the Google docs spreadsheet Robert set up.

This gets the calculated profiles noticeably closer to those calculated by
other software, except for the multi-level dive (20m for 10min, then drop
to 60m for 30min).  I think the small difference might be related to use of
Schreiner vs Haldane equations in the change in levels, but could be wrong.

Note that this change alters the first_stop_pressure used for the Boyle's
law compensation.  The way the profile is calculated, if we get to that
depth but can ascend to the next, then we do.

Rick
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