What you need

Steps

On the Bench screen, choose the aircraft under Save measurements to, then tap Throw meter.
Under Surface, choose the surface, such as Aileron (left), and enter the surface chord.
Lay the iPhone flat on the surface, top toward the trailing edge, with the stick centered.
Wait until the reading says Stable, then tap Zero.
Move the stick so the surface goes fully up. Wait for Stable, then tap Save as up.
Move the stick so the surface goes fully down. Wait for Stable, then tap Save as down.
Repeat for each surface. Type a different rate name, such as Low, to save a second set.
Tap Saved throws on the Bench screen to compare the left and right surfaces.

Set end points and rates on your transmitter first, so the linkage doesn't bind.
Surface chord is measured from the hinge line to the trailing edge. It turns degrees into travel.
Turn on Hold to freeze the reading, so you can let go of the stick before you look.
If the surface is too narrow for the iPhone, lay it along the hinge and change the iPhone position.
Tap Announce to hear the reading aloud.

The reading keeps moving: Keep the model still and the iPhone flat. Center the stick and tap Zero again.

Throw: How far a control surface moves from center, in degrees or as travel at its trailing edge.
Rates: Throw settings you switch between on the transmitter. Low rates are gentler for normal flying, and high rates are for aerobatics.
End points: The transmitter setting that limits how far each servo moves, so the linkage doesn't bind.
Hinge line: The line a control surface pivots on.
Chord: The width of a wing or control surface, from its leading edge to its trailing edge.
Trailing edge: The back edge of a wing, stab or control surface.