Your phone is the tool
Level & Ruler
Your phone asks before it shares its tilt with a page. The readings stay on your phone.
Hold a bank card flat on the screen, tucked into the corner at zero. Drag until the outline's far end meets the card's.
Hanging a picture? Rest the phone's long edge on top of the frame. You'll hear a soft click when it's level, which helps when the frame is above your eyes.
No phone is perfectly true. Calibrate does the carpenter's check: read it, turn it end for end on the same spot, read it again. The difference cancels your phone's own error and tells you how far off the surface is.
The ruler is true once you set it with any bank card or a quarter. It's saved for this screen.
Motion readings and measurements stay on your device. Nothing is sent anywhere.