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Fix ATM-vs-bar confusion

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SAC should be calculated in relationship to surface pressure, not "1 bar".

I also realize that we have a few other cases where we do the same
mistake: the partial pressure calculations do things like

    po2 = o2 / 1000.0 * depth_to_mbar(sample->depth.mm, dive);

which is wrong as well - the partial pressure is also relative to
standard atmospheric pressures.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
This commit is contained in:
Linus Torvalds 2014-02-11 13:08:29 -08:00 • committed by Dirk Hohndel
parent 92bbed3304
commit e58f54cac1
4 changed files with 16 additions and 6 deletions
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10
dive.h
View file

@ -223,6 +223,11 @@ static inline double bar_to_atm(double bar)
return bar / SURFACE_PRESSURE * 1000;
}
static inline double mbar_to_atm(int mbar)
{
return (double) mbar / SURFACE_PRESSURE;
}
/* Volume in mliter of a cylinder at pressure 'p' */
extern int gas_volume(cylinder_t *cyl, pressure_t p);
extern int wet_volume(double cuft, pressure_t p);
@ -450,6 +455,11 @@ static inline int depth_to_mbar(int depth, struct dive *dive)
return calculate_depth_to_mbar(depth, dive->surface_pressure, dive->salinity);
}
static inline double depth_to_atm(int depth, struct dive *dive)
{
return mbar_to_atm(depth_to_mbar(depth, dive));
}
/* for the inverse calculation we use just the relative pressure
* (that's the one that some dive computers like the Uemis Zurich
* provide - for the other models that do this libdivecomputer has to

6
divelist.c
View file

@ -221,7 +221,7 @@ static int calculate_otu(struct dive *dive)
po2 = sample->po2;
} else {
int o2 = active_o2(dive, dc, sample->time);
po2 = o2 / 1000.0 * depth_to_mbar(sample->depth.mm, dive);
po2 = o2 * depth_to_atm(sample->depth.mm, dive);
}
if (po2 >= 500)
otu += pow((po2 - 500) / 1000.0, 0.83) * t / 30.0;
@ -285,7 +285,7 @@ static int calculate_cns(struct dive *dive)
po2 = sample->po2;
} else {
int o2 = active_o2(dive, dc, sample->time);
po2 = o2 / 1000.0 * depth_to_mbar(sample->depth.mm, dive);
po2 = o2 / depth_to_atm(sample->depth.mm, dive);
}
/* Find what table-row we should calculate % for */
for (j = 1; j < sizeof(cns_table)/(sizeof(int) * 3); j++)
@ -338,7 +338,7 @@ static int calculate_sac(struct dive *dive)
return 0;
/* Mean pressure in ATM (SAC calculations are in atm*l/min) */
pressure = (double) depth_to_mbar(meandepth, dive) / SURFACE_PRESSURE;
pressure = depth_to_atm(meandepth, dive);
sac = airuse / pressure * 60 / duration;
/* milliliters per minute.. */

2
profile.c
View file

@ -226,7 +226,7 @@ static int get_local_sac(struct plot_data *entry1, struct plot_data *entry2, str
/* Mean pressure in ATM */
depth = (entry1->depth + entry2->depth) / 2;
atm = (double) depth_to_mbar(depth, dive) / SURFACE_PRESSURE;
atm = depth_to_atm(depth, dive);
cyl = dive->cylinder + index;

4
qt-ui/maintab.cpp
View file

@ -475,7 +475,7 @@ void MainTab::updateDiveInfo(int dive)
volume_t sac;
QString SACs;
if (mean[0] && duration[0]) {
sac.mliter = gases[0].mliter * 1000.0 / (depth_to_mbar(mean[0], d) * duration[0] / 60.0);
sac.mliter = gases[0].mliter / (depth_to_atm(mean[0], d) * duration[0] / 60.0);
SACs = get_volume_string(sac, true).append(tr("/min"));
} else {
SACs = QString(tr("unknown"));
@ -483,7 +483,7 @@ void MainTab::updateDiveInfo(int dive)
for(int i=1; i < MAX_CYLINDERS && gases[i].mliter != 0; i++) {
volumes.append("\n" + get_volume_string(gases[i], true));
if (duration[i]) {
sac.mliter = gases[i].mliter * 1000.0 / (depth_to_mbar(mean[i], d) * duration[i] / 60);
sac.mliter = gases[i].mliter / (depth_to_atm(mean[i], d) * duration[i] / 60);
SACs.append("\n" + get_volume_string(sac, true).append(tr("/min")));
} else {
SACs.append("\n");