Spirit Level: Ruler & Angle

Four instruments on the phone that is already in your hand.

A shelf to hang, a picture to straighten, a ramp to check, a label too small to read. The phone has the sensors for all four, and this app is the dial on top of them.

What it does

• Spirit level. Lay the phone on a surface or hold it against a wall — it knows which of the two you are doing and shows the bubble for that posture. Accept as zero takes out the tilt the camera bump adds, so the reading is about the shelf rather than about the phone.
• Clinometer. The slope in degrees and in per cent at the same time, because a ramp is specified in per cent and a roof in degrees. 45° is 100%.
• Ruler. A scale drawn to size on the glass, in millimetres and centimetres or in sixteenths of an inch. It knows the pixel density of your screen; if it does not, it asks you to lay a bank card on it once — every payment card in the world is 85.6 mm along the long edge.
• Magnifier. The camera with the zoom pulled up and the torch to hand, for dosages, serial numbers and ingredient lists.

What it is honest about

This is an approximate instrument, not a certified one. It reads the phone's own sensors, and a phone is not a machinist's level. Use it to hang a shelf; do not use it to settle an argument with a building inspector.

Free and paid

The level is free and stays free. The app shows ads between openings, and one payment — no subscription, nothing renewing — removes them and unlocks whatever is locked for you. Restoring a purchase on a new phone is a button in Settings.

Nothing of yours leaves the phone

No account, no sign-in, no server of ours. Measurements stay in the app's own storage. Ads are served by Google and purchases handled by Apple — what they see is on the privacy page.