What the measurement can tell you
A Room Tuner reading is a practical guide to your listening setup, not a laboratory certificate. Here is the line between what it measured and what it did not.
What it directly measures
The curve shows how strongly each frequency reached the iPhone at your listening position while your system played the test sweep. The score compares that measured shape with your chosen target. It is not a loudness score.
What is relative
The result describes your speakers, room, phone and setup together. Room Tuner is not a calibrated sound-level meter, so it does not claim an absolute dB SPL, Noise Criterion or hearing-safety reading.
When two readings can be compared
Keep the phone position, main volume, target, microphone setting and playback setup the same. If the method, audible range or setup changes too far, both readings remain useful on their own, but Room Tuner will not call one better.
When it refuses
Background noise can hide part of a sweep. Two speaker paths can be too similar to separate. A capture can also be clipped or interrupted. In those cases the app names what remains valid and leaves the unsupported conclusion unmeasured.
What it never diagnoses
Room Tuner does not test your hearing, certify room dimensions, identify a damaged speaker, infer physical left and right from the microphone, or prove that one treatment caused a change. A physical-side label appears only when you confirm what you heard.