Support
Trueplane for iPhone
Questions, bug reports and suggestions are welcome by email:
Please include your iPhone model and iOS version. Replies usually within a few working days.
Frequently asked
The reading is not exactly zero on a surface I know is level.
That is your device's factory sensor offset, and it is normal. Run
Settings → Accuracy → Calibrate device. You measure the same
spot twice with the phone turned 180° in between, first lying flat and then
standing on an edge. The surface you use need not be level — only flat and
firm.
Why does it ask for an upright position as well?
Because the camera housing stands proud of the back. Lying flat, the phone
rests on the housing rather than on the surface, which tips it by a couple of
degrees. That tilt is real and belongs in a flat reading, but it has no place in
an upright one. Measuring both positions keeps them apart. It is also why a
phone laid on its back on a worktop will read a degree or two off unless it is
calibrated that way — measuring on an edge, or with a case that clears the
housing, avoids it entirely.
Does the calibration stay valid?
Mostly. Sensors drift with temperature by roughly a tenth of a degree per
10 °C, so a calibration done indoors is slightly off outdoors in winter.
If you need the last tenth of a degree, calibrate near the temperature you work
at.
What is the difference between Set Zero and Calibrate?
Calibrate corrects the instrument — it removes your phone's own error, once per
device. Set Zero changes what you compare against — it declares the current
surface to be zero, so you can match one surface to another. Tap the info badge
next to the mode or reference indicator in the app for a short explanation of
either.
What does a negative reading mean?
Plus means the right or top edge is the high side; minus means it falls away the
other way. The bubble always drifts toward the high side, like a real spirit
level.
How accurate is it?
Sensor noise on a modern iPhone sits around 0.02–0.05°. While the device rests
still and the status reads “Steady”, averaging reduces that by roughly
a factor of ten. Moving in the hand, expect considerably less.
The numbers change too quickly to read.
Settings → Readout refresh. Each update shows the average over its
interval, so a slower setting is both calmer and more accurate. The vial keeps
tracking live regardless.
Can I get my measurements out of the app?
Yes. History → share icon exports everything as CSV, in degrees.