Well, plus or minus one EV is pretty awful for any alleged meter.
It doesn't mean that you are either 1 over or 1 under, but somewhere between, most often the lightmeter-app is correct and if it's off, it has been shown to be a max at +- 1 ev.
My experience is that it struggles when shooting against the sun (camera-lens gets flare or whatever) and in low-light situations where the phone-camera (doesn't) isn't supposed to work very well anyway.
Basically, it will, for the most part, give you a true reading and most shots on a roll will come out fine.
If you are Ansel Adams, you carry a spot-meter and calculate (probably on paper, with a mathematical ruler) the theoretically correct exposure, and that's ok I guess.
I've got a better idea. Carry a real light meter and leave the obnoxious cell phone
behind.
Why should people start leaving their mobile (note the name) phones at home, just because they go out to take photos?
It's ok
not to use this feature if one so wish, but ditching the whole phone?
The era of signal-fires on top of mountains has passed you know (very few people will understand if you need help for example).
