Use a neutral reference
Choose a matte, neutral gray or white surface in the same light as your object. Tap Calibrate or press and hold the circle. Very bright, dark, colored or uneven surfaces are unsuitable.
Recalibrate when conditions change
Calibration applies to the current situation. It resets when you toggle the flashlight, leave the app or the camera readjusts. Calibrate again after a change in lighting or after 60 seconds.
Use the flashlight thoughtfully
The lamp control switches your iPhone flashlight on or off. With the light on, measure from around 30–40 cm (12–16 inches). Avoid shiny patches: reflections can hide color information.