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• ## Re: How do I set the Relative Air Pressure - calculation?

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• Hi, I can only work from the absolutes here! 1013.25hpa = 1 atm (atmosphere). The pressure at sea level on a normal day with clear weather and no changes
Message 1 of 5 , Nov 20, 2007
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Hi,
I can only work from the absolutes here! 1013.25hpa = 1 atm
(atmosphere). The pressure at sea level on a 'normal' day with clear
weather and no changes taking place.
So if I take the calculation I made, and apply it on a clear bright
day... - I am at 1500 feet, or the equivelant in meters. So its
962.86 ... although someone will probably tell me I'm wrong. :-)

cheers
Rob

--- In wuhu_software_group@yahoogroups.com, "Bill Graves"
<bill.graves@...> wrote:
>
> Now this is where I find a problem with this unit -
>
> The unit is reading absolute pressure which is the atmospheric
pressure at
> my Altitude 250Ft above sea level(Or so the instructions claim), the
> Airfield next to us(Also at 250ft above sea level) from which I fly
is
> reading a higher Atmospheric pressure than the unit. To set the
relative
> pressure to sea level for example I should be increasing by about
8Hpa(1 Hpa
> per 30 feet altitude) as obviously there is more pressure at sea
level.
>
> However as I know the unit is not reading the correct Absolute
pressure and
> I cannot calibrate it to do so, all I can assume is changes in
pressure up
> or down - the accuracy is not good.
>
> So what I am saying shanghai_bob_dog is that while your calculation
is
> correct for you at 1500m altitude - the pressure would only be
correct if
> the absolute pressure you are subtracting from was the pressure at
sea level
>
> So what you have to do is find out exactly what the pressure is at
your
> altitude and set this as the relative pressure - ignoring what the
absolute
> pressure is saying as this is pre set and will stay fixed relative
to your
> "relative" pressure.
>
>
> -----Original Message-----
> From: wuhu_software_group@yahoogroups.com
> [mailto:wuhu_software_group@yahoogroups.com] On Behalf Of
wuhu_software
> Sent: 19 November 2007 15:06
> To: wuhu_software_group@yahoogroups.com
> Subject: [wuhu_software_group] Re: How do I set the Relative Air
Pressure -
> calculation?
>
>
>
> Robert,
>
> Yes, you need to set the relative pressure on the console itself.
>
> Where are you obtaining the relative pressure for your area?
>
> Check on Weather Underground for a station that is near you.
>
> --- In wuhu_software_ <mailto:wuhu_software_group%40yahoogroups.com>
> group@yahoogroups.com, "shanghai_bob_dog"
> <shanghai_bob_dog@> wrote:
> >
> > Adding to my first post. I forgot to mention that I am using hPa,
> and
> > 1500ft is actually 457.2 meters.
> >
> > the atm = 1013.25 hPa
> > the altitude = 457.2 meters
> >
> > Currently my Ws3600 relative pressure is set to 1013.25 -
obviously
> not
> > correct.
> >
> > Now, I found a post that gives this deal in imperial
measurements.
> > Pressure drops .001 inHg / Foot of altitude
> > So 1500 feet = 1.5 inHg
> > and if I multiply this by 33.86 to get hPa = 50.79.
> > So - I should subtract this from 1013.25, which equals 962.86
> >
> > Now this is odd, because the WUHU software is reporting an
Absolute
> > pressure that ranges around this.
> >
> > So - Do I actually set the Relative Pressure on the WS3600 to the
> > 962.86 setting - and then everything else falls into place ?
> >
> > well - lets suck it and see :-)
> >
> >
> >
> >
> >
> > --- In wuhu_software_ <mailto:wuhu_software_group%
40yahoogroups.com>
> group@yahoogroups.com, "shanghai_bob_dog"
> > <shanghai_bob_dog@> wrote:
> > >
> > > I'm trying to figure out just what is meant by setting the
> Relative
> > > Pressure setting on my WS3600
> > >
> > > I am at 1500 ft abouve sea level. This apparently has something
> to do
> > > with the setting.
> > > The display reads a relative setting and an absolute setting on
> the
> > > WS3600. So what should I actually set the devices setting to -
> > > supposing that I am actually supposed toset it.
> > > thanks
> > > Robert
> > >
> >
>
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