With Bubble you can measure angles and inclination.
Hold one of the four sides of the phone against an object or place it on a flat surface to check the orientation.
No permissions required
This is an updated version (Target SDK 30) of https://f-droid.org/de/packages/net.androgames.level/ which has not been revised since 2014.
An Android Bubble Level application.
Copyright (C) 2014 Antoine Vianey
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Level is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with Level. If not, see <http://www.gnu.org/licenses/>