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

Dirk Hohndel dirk at
Fri Jan 11 07:00:32 PST 2013

"Robert C. Helling" <helling at> writes:

> 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.

Well... you are the Chief Scientist... :-)

But all kidding aside, I'm a bit nervous about this one. I think I'd
rather have us use the math as it is defined and have the people who
want to be more aggressive do so on their own.


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