Graph documentation [was: Re: Meaning of GF settings]

Robert C. Helling helling at
Fri Jan 11 06:42:50 PST 2013

On Fri, 11 Jan 2013, Dirk Hohndel wrote:

> #define  DIST_FROM_3_MTR         0.28
> if (mydata.pressure > mydata.surface)
> {
>       pressure = 3 * (unsigned int)((mydata.pressure - mydata.surface + DIST_FROM_3_MTR) / 0.3);
>       mydata.pressure = ((float)pressure)/10 + mydata.surface;
> }
> This clearly chops off the last bit of 'tail' in the shallow part. It's
> not a lot (0.02 bar - about 20cm), but my guess is this helps to shorten
> especially the last stop.

I had to look at this for a while to understand what it's doing: It adds 
the pressure equivalent of 2.8m to mydata.pressure and then rounds to the 
next smaller multiple of 3m, i.e. depths 0-0.2m are rounded to 0 while 
0.2m-3.2m are rounded to 3m, 3.2m-6.2m to 6m etc. So in effect it treats a 
ceiling (as mydata.pressure will later become the ceiling) of anything up 
to 20cm as 0. So, yes indeed, this is the "different way of rounding" that 
I was talking about.

Do we want to do the same? We could equivalently always subtract 200mm 
from our ceiling ;-) Or at least for the planning part of the code.


Robert C. Helling     Elite Master Course Theoretical and Mathematical Physics
                       Scientific Coordinator
 		      Ludwig Maximilians Universitaet Muenchen, Dept. Physik
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