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It would be averaging the effects of measurement (pseudorange) imprecision 
(random over longish time intervals) and multipath (not random and not 
repeatable except for a fixed location with the same satellites one sidereal 
day to the next). And, to a lesser extent, tropospheric delay errors and 
other minor model deficiencies. Two sites, some distant apart, would 
experience different errors although the pseudorange-based DGPS technique 
(such as that supported by the Coast Guard) uses the errors computed at a 
reference station to improve the positions of a rover (in real time).
-- Richard Langley

On 2013-04-10, at 1:20 PM, Marcel Tschudin wrote:

> 
> Thank you, Brad, for finding this Android app for me. I presume that
> the 1 m represent an absolute accuracy and that measurements of height
> differences may possibly attain a higher accuracy. I will give this
> affordable gadget a try and perform some tests with it.
> 
> Marcel
> 
> 
> On Wed, Apr 10, 2013 at 6:28 PM, Brad Morris 
>  wrote:
> > ________________________________
> >
> > Hi Marcel
> >
> > There is an app in the Android market called "Precision GPS Pro".  The cost
> > is US$0.99
> >
> > It claims a 1 meter elevation accuracy after averaging, although they do not
> > indicate how long an average you require to achieve that.
> >
> > The free version of this app does not do elevation averaging.
> >
> > I have not tried this app.
> >
> > Brad
> >
> > On Apr 9, 2013 6:21 AM, "Marcel Tschudin" 
>  wrote:
> >>
> >> ________________________________
> >>
> >> In my sunset observations the guesstimates for the HoE of probably not
> >> better than +/- 20% are indeed a weak point. But how weak? The dip is
> >> proportional to the square root of the HoE which means that the
> >> estimated dip error is only half of the estimated HoE error. For the
> >> average HoE of 3.5m the "normal" dip is 3.3 moa and a 10% error of it
> >> therefore +/- 0.33 moa. This corresponds in the photo to slightly more
> >> than one pixel which is 18 seconds of arc.
> >>
> >> Frank, you mentioned estimating HoE within about +/-5%. I'm wondering
> >> whether you would also be able to attain such an accuracy by climbing
> >> over the rocks as shown in my photo:
> >>
> >> 
https://mail-attachment.googleusercontent.com/attachment/u/0/?ui=2&ik=b33d2c81ba&view=att&th=13ddab531282f2e7&attid=0.1&disp=inline&realattid=f_hf5h7cfp0&safe=1&zw&saduie=AG9B_P-DvbGAuAxTxtruQd29-avq&sadet=1365502394438&sads=w4N-7jPt0vbdfN6eZHKSEaR8vQ0
> >> For my average of 3.5 m this would correspond to less than 20 cm or
> >> what might be more familiar to you to about half a foot.
> >>
> >> In order to verify my guesstimates I do indeed consider to perform
> >> some additional measurements. I'm wondering how good I could measure
> >> it using GPS and also the Russian version of it. I have no experience
> >> in using these systems. I understand that I would have to measure both
> >> levels, eye and sea level and then take the difference. Is there an
> >> Android application which I could load on my Samsung pad allowing to
> >> collect measurements over a longer time period which then calculates a
> >> mean altitude and its standard deviation? What are the sort of result
> >> one could obtain this way?
> >>
> >> Marcel
> >>
> >> : http://fer3.com/arc/m2.aspx?i=123477
> >
> > : http://fer3.com/arc/m2.aspx?i=123498
> 
> 
> : http://fer3.com/arc/m2.aspx?i=123499
> 

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| Richard B. Langley                            E-mail: lang@unb.ca         |
| Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/ |
| Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142   |
| University of New Brunswick                   Fax:      +1 506 453-4943   |
| Fredericton, N.B., Canada  E3B 5A3                                        |
|        Fredericton?  Where's that?  See: http://www.fredericton.ca/       |
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