[lug] OT: android elevation app accuracy

[Davide Del Vento]

Thanks for all these suggested (which of course I knew already, being
a physicist by training.

They are all very unpractical for what I need to do, because the
corners are opposite and not in sight, the gutter is not level (and
has a large "gap") and there is lots of additional small tricky
details. The only feasible technique would be the bucket with the
hose, but by no means easy or quick.

Regarding the joke, that was probably true in the old times, but now
things are different. Air pressure is about 84kPa at our altitude and
here there is a differential of about 1kPa every 100m (330 ft).

A barometer such as this http://www.omega.com/pptst/HHP360.html claims
to be able to measure 0.015% or 0.01kPa or 1m (3ft) of ABSOLUTE
pressure. So it can certainly measure the height of a building even if
it's not as tall as a skyscraper! It can't go down to inches as
absolute pressure, but maybe it can go there for relative one, which
is what I need. However it's too expensive to try (or even spending
time reading its specs to understand).

According to http://what-if.xkcd.com/64/ an Android device is able to
measure the pressure difference between head and feet of a person, so
that's why I asked here in the first place: maybe it can measure an
inch. Has anybody tried?

Thanks!
Davide

On Sun, Sep 29, 2013 at 4:48 PM, Bear Giles <bgiles at coyotesong.com> wrote:
> Actually I just remembered a second approach. If you can run a hose between
> two buckets of water you can use it as a level. You'll need to make sure
> that the hose is completely full so the water can freely flow between the
> buckets but other than that it's a matter of putting the buckets on each
> corner of the building and figuring out a way to measure the height of the
> water to what you're trying to check.
>
>
> On Sun, Sep 29, 2013 at 4:40 PM, Bear Giles <bgiles at coyotesong.com> wrote:
>>
>> This reminds me of the old physics major joke about how you determine the
>> height of a skyscraper with a barometer.
>>
>> A: find the building super and tell him you have a neat barometer for him
>> if he tells you the height of the building.
>>
>> You'll need a level. A barometer isn't going to cut it, not even remotely.
>>
>>
>> On Sun, Sep 29, 2013 at 4:35 PM, Jed S. Baer <blug at jbaer.cotse.net> wrote:
>>>
>>> On Sun, 29 Sep 2013 16:28:03 -0600
>>> Jed S. Baer wrote:
>>>
>>> > > i.e. how much slope there is, if any,
>>> > > between these two corners
>>> >
>>> > I think your best bet will be to use a string level. Or, a 4 foot or
>>> > longer beam level, working along your gutter.
>>>
>>> Or,
>>>
>>> http://www.homedepot.com/p/Johnson-Hand-Held-Sight-Level-80-5556/202911589
>>> http://www.homedepot.com/p/Johnson-Torpedo-Laser-Level-40-0915/202258085
>>>
>>> Might be you know someone who has a laser level already?
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>>
>
>
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