Datum: Spirit & Bubble Level

Datum is a spirit level and bubble level for your phone, with a ruler and a protractor in the same app, from Moonlet Labs. Spirit level and bubble level Lay the phone on a shelf, a picture frame or a worktop and read the tilt in degrees, to one decimal place. Bullseye is a round bubble level that shows both axes at once. Bar is a single-axis spirit level that reads whichever edge is nearer horizontal, so it also works with the phone stood on its edge against a post or a door frame. When the surface is level, the ring turns green and the phone gives a short vibration, with an optional beep. Hold freezes the reading so you can check it after lifting the phone, and the rotation lock keeps the screen from turning while you work. Calibrate to your phone A phone's sensor can be slightly off. Put the phone on a surface you know is level, tap Calibrate, and Datum remembers the offset. The steadiness setting lets you choose a quicker or a calmer bubble. Ruler Measure small objects against the screen in millimetres or inches, with a measuring line you drag or tap into place. The ruler uses the screen size your phone reports, so it works straight away. If your phone reports it wrongly, calibrate once by fitting an outline to a bank card. The ruler is as long as your screen, and Datum shows how far it reaches. Protractor and angle finder In Touch mode, hold an object to the screen and drag two arms along its edges to read the angle between them. In Tilt mode, lay the phone's long edge on a ramp, a stair rail or a sloping board and read its angle from horizontal, like an inclinometer. Datum never uses the camera. Datum works in portrait and landscape and opens on the last tool you used. Privacy: no account needed. All measuring features work offline, and sensor readings stay on your phone. The app is ad-supported: ads are served by Google AdMob, which may use the advertising ID. Moonlet Labs collects crash reports and usage analytics through Google Firebase, linked to pseudonymous app identifiers rather than your name or email. Where the law requires it, the app asks for your consent first, and privacy choices are in Settings. Privacy policy: moonletlabs.com/privacy.html