It wouldn’t matter… just tell the user to close and open the lid before pressing enter again, and get the maximum (or minimum) value as the lid being close all the way.

like the answer to any other similar question, with a prompt?

Prompt for what? A Key press?

You really can’t solve this on your own?

You could use the camera to estimate if the laptop is closed.

Exactly my thought, but this might not be precise enough in low light conditions? So maybe best used as a fail safe (if camera is lit don't calibrate even if the user pressed confirmed)