Hi, I have retry and make some re-calibration but it seems impossible to get a decent precision. On a perfect piano It still get 1grade error

Thanks for tour replay.
I have follow this step:
Get into menù with *#87#
Select voice item_test
Then select g-sensor

After finish all nothing have changed,

Hi, I have same problema with BV5500 Pro, how is possibile to solve or calibrate? I attach a photo where the plumb tool is out of 4°