In order for OdySight to detect a change in how you perform on the test from one day to the next, you must do the tests under similar conditions each time.
Therefore, the app is continually checking:
The ambient light. Try to do your tests in a well-lit room, with no direct light on your face or on your device. If the room is too dark or too bright, the app will tell you to find another location to the test.
The distance to screen. During the tests, the distance between your device and your face must be between 35 and 45 centimeters. This distance is checked before and during the tests.