On Sunday, December 18, 2016 at 12:18:40 AM UTC-6, micky wrote:

I need a compass app and the Play store has loads, but about half of
them say that the phone has to have a magnetometer, and from gsmarena,
it seems my Blu phone Android v.5 does not
( http://www.gsmarena.com/blu_studio_x_plus-6926.php )

Some of them have in big print that a magnetometer is needed and others
say nothing. One of them that seemed really good finally said 21 lines
in "Large iron and steel objects can influence the magnetic sensor in
your Android device, " https://play.google.com/store/apps/details?id=com.gamma.compass

So, do some not require a magnetometer?

If they don't require one, do they require nearby cell towers? Some
of my driving won't be in cell tower range. At least the coverage map doesn't show coverage.

Is there some 3rd or 4th way that a compass app can figure out
direction? (Are the answers to this the same as to "What is needed for
GPS to figure out location?")

I could just install some and go out to where there is no cell coverage
and see if they work, except that when I signed up 7 or 10 years ago
there were areas like that for AT&T only 20 minutes away. Now their
coverage map shows only small areas 2 hours from here, and the areas are
in the mountains and so small I don't think I can find them, especially
on foot, which I would have to be.

TIA

In the very near future, I will be introducing the world’s only correctable (compensated for residual [after calibration] azimuth deviation errors) smartphone compass app. With the introduction of my new smartphone (iPhone & Android) app, users will
be able to evaluate the accuracy (or lack thereof) of any electronic compass, rangefinder compass, and/or smartphone compass app - with the results being made available to immediately correct residual azimuth deviation errors of the evaluated compass app
or electronic compass.

I am offering you (vendors) the opportunity to correct residual azimuth deviation errors generated by your own smartphone compass app. The azimuth error correction process is quite simple; and you will not need to significantly modify your app. If you
may be interested in taking me up on this offer, please contact me.

Also, please take a look at tru-path.org (and its various blog posts) to see actual test results of several iPhone compass apps (and rangefinders) demonstrating the magnitude and direction of real, significant residual azimuth deviation errors - along
with the error correction results. Correcting smartphone residual azimuth deviation errors is fast, easy, and entirely practical using today’s smartphone technology. My next set of tests will be performed on Android compass apps; and, based on
existing published user questions and comments, I expect to find results similar to those already posted.

Thanks for your time and consideration.

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