Apple iPhone iOS 8.1 - Manual (Page 136)

Chapter 30 Compass 136
On the level
On an edge ... On an edge ...
... or lying flat ... or lying flat
Deviation
from level
Deviation
from level
Level! Level!
Deviation from
chosen slope
Deviation from
chosen slope
Show the level. Swipe left on the Compass screen.
Hang it straight. Hold iPhone against a picture frame or other object, then rotate them until you
see green. For true level, the deviation is displayed on a black background. If the background is
red (indicating relative slope), tap the screen to change it to black.
Level the table.
Match that slope. Hold iPhone against the surface you want to match, then tap the screen to
capture the slope. The slope you seek is shown in black, with deviation shown in red. Tap again
to return to standard level.