I figured a light meter app on my phone was a joke until I missed 8 frames on a roll of Portra 400
For 2 years I refused to touch my phone while shooting, it felt wrong and I trusted the meter in my Nikon FM2 with my life. Then last month in Santa Fe I shot a whole roll at dusk and every single frame came out muddy, so I finally downloaded one of those free meter apps just to compare. It matched my in camera meter within a third of a stop in every lighting setup I tried, and it saved my butt shooting indoors at a diner with no window light. Has anyone else tested a phone meter against a handheld Sekonic, because I want to know if I am fooling myself.
Watched a YouTube guy run a test where he put a phone meter up against a Sekonic in like six different lighting setups and the phone was never more than half a stop off, which honestly surprised me since I always figured those apps were just guessing. He did say the phone struggled a bit with backlit stuff and really dim scenes, so it is not perfect, but for normal shooting it held up fine. My FM2 meter has been solid too, but those old center weighted meters can get fooled pretty easy when the light is weird or the scene has a big bright sky in it. Phone meters do spot or average readings depending on the app, so they can actually be smarter than what is built into an old camera. Half a stop does not matter much with Portra anyway since that film has so much room to play with. If your test matched within a third of a stop I would trust it and stop worrying about it.