Using cellphone apps for measuring magnetic fields?

[searcher]

I'm looking for opinions on using cell phone apps during an investigation to measure magnetic fields, compass direction, elevation
and azimuth. After all, there is no information on how they're calibrated, if at all, and no information on how accurate they are. I've spoken with two MUFON staff. One says cell phone data tracks VERY well with calibrated instruments and another says he could get NO correlation between the two. At least the Tri-Field meter has an accuracy spec of +/- 30%, which is useful as long as it's taken into account when drawing conclusions from its data.

I firmly believe we investigators ought NOT be using cell phone apps to document investigations. Comments?

[tobiasclaren]

Hmmm, for detecting a gravimetric anomaly, the smartphone would have to be fixed.
these apps seems very accurate, I can see ~"9,81N" .

Here is my suggestion for a sensor network, paid by private persons:
mutualufonetwork.proboards.com/thread/1026/network-based-gravimeters-magnetometers-server

With the sensors in smartphones, or perhaps more sensitive in future from vr goggles like Rift and Vive...

[searcher]

I have seen what appears to be a reasonable theodolite app here www.macobserver.com/tmo/review/theodolite_app_for_ios_is_breathtaking
My next question is what is the CHEAPEST cell phone that has the sensors to work with this app?