Meter app in my mobile VS Nikon fm2 meter. Which one should i trust?

Meter app in my mobile VS Nikon fm2 meter. Which one should i trust?

Added (1). for example:
light meter app shows ISO200 f2 T250
but FM2 goes negative with the same setting

The Nikon's meter is TTL, so it works on what the lens sees - any meter reading can be inflated by reflective surfaces, too much sky etc.

I've used a REAL hand-held meter in tricky situations (the palm of your hand is an excellent indicator, as is the ground) but generally I'd trust the TTL meter most of the time - experience is the only way to find out differently.