How do you measure front-to-back tilt?
Point the top edge of the phone in the direction you want to measure. This might be up a ramp, out from a wall, or along a worktop.
Lay the phone flat and tap Check Tilt. The bubble moves toward the higher end, and the label beside the vial names that end.
This is the direction a side-to-side level cannot measure. A shelf can be level across its width and still tilt forward.
A forward tilt of only 1° is about 17 mm over one metre. That is enough to move a cup toward the edge over time.
How do you measure a slope that is meant to be there?
Drainage falls, ramps and gutters are built with a deliberate slope. These are not specified in degrees.
Use Slope for percent and Drop per metre for millimetres. A patio usually needs about 12 mm of fall per metre away from the building.
On a run longer than the phone, rest the phone on a straight batten. The phone measures only the 15 cm it sits on, so a single dip can look like the slope of the whole run.
For falls written as a ratio, such as 1:80, the Inclinometer shows the ratio directly.