[lug] OT: android elevation app accuracy

[Carl Wagner]

Davide,

I am with John on this.  A water level with a helper or a 
transit/builders level could probably get you to 1/4" (abound 6 mm) or 
possibly better .
How far apart are the corners?   I have a one person water level that I 
could loan you (it beeps when the water level on the remote end is at 
the same height as the sensor).    I think the hose is 50' long and it 
can be extended with a garden hose but you would need to buy the hose 
adapters from a place like Home Despot or McGuckin's (I "think" it is 
3/8" clear plastic tubing so you would need a male hose to 3/8" barbed 
and a female hose to 3/8" barbed. Plastic adapters would work fine and 
are cheap.).  As others have said, make sure you get all the larger 
bubbles out.

http://www.physicsforums.com/showthread.php?t=182965

I am coming up with a blank on how to make this Linux related though.  ;-)

Carl



On 09/30/2013 11:33 AM, John Hernandez wrote:
> Davide, use a string level or water level to establish a level
> reference line.  Corners and other limitations may require you to
> establish new points of reference as you proceed, but it shouldn't
> take more than 15 minutes to go around the whole house with a helper.
> An easy way to measure deltas is to create a story pole with a scrap
> of lumber.
>
> It's also good idea to double check bubble or laser levels using the
> water & tubing method described in other posts.
>
> On Mon, Sep 30, 2013 at 9:03 AM, Davide Del Vento
> <davide.del.vento at gmail.com> wrote:
>> 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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