Per-Device Calibration via 18% gray
Point at a gray card in direct sun, tap once, and dial out your sensor's offset.
Where to find it
Settings Calibration Run Test
Summary
Calibrates the meter to your specific phone. A live preview shows exactly what you are pointing at; fill the frame with a gray card or an average matte subject in direct sun, tap once, and the app captures an offset that applies to every reading from then on. You can also match a handheld reference meter or type an offset by hand.
Detail
How it works
What it does
Phone camera sensors vary slightly from one device to the next, even within the same model. This step measures your phone's offset against a known reference and applies it to every future reading so the numbers match what a dedicated meter would say.
What to point at
Point the camera at a gray card in direct sunlight, with the sun behind you. A plain gray wall, or any evenly lit medium-gray surface, works too. Fill the whole frame with it, because the meter reads the entire frame. Avoid anything white, black, or shiny, stay out of shadows, and never aim at the sky or the sun, since those throw the reading off by a stop or more.
How to run it
Open the calibration dialog and watch the live preview while you aim. Tap Run Test, hold steady, and the app compares what it read to the Sunny 16 reference. Review the proposed offset and tap Apply. The number shown is exactly the offset that gets stored.
Match another meter
If you own a handheld meter such as a Pentax spot meter, switch the reference to My Meter, point both at the same scene, and enter the aperture, shutter, and ISO your meter recommends. The app converts that to the reference brightness and calibrates the phone to agree.
Set the offset by hand
The advanced row lets you type an offset directly in stops. A positive value brightens every reading, a negative value darkens it. Useful when you already know your correction or want to nudge it.
When to re-run
Once is enough for most users. Re-run if you switch phones, if you change a major Camera2 setting (Pro precision toggle, AWB), or if you suspect the readings have drifted. The offset is stored per profile so different cameras you switch between can have different offsets.
What it does not do
It cannot fix lens variation between different cameras you might attach to the phone. The offset corrects sensor behavior, not optical quirks. For lens-specific compensation, use the filter factor or expired-film modal.