What you need

Steps

Open Bench and tap Tape measure. Or, on the aircraft's page, tap Measure wingspan with camera.
Under Size, choose what to measure, such as Wingspan.
Stand about an arm's length from one wingtip. Move the iPhone slowly until the dot turns yellow.
Aim the dot just inside the tip, on the model itself, and tap Set start.
Move to the other tip, aim just inside it, and tap Set end.
Measure two or three times. Maiden averages the readings.
Tap the Save button to store the average on the aircraft.

Plain or shiny surfaces are hard to track. A strip of masking tape at each end helps.
If the readings are far apart, a point probably landed on the floor behind the model. Measure again.
To remove a reading, tap the remove button next to it.
On a model with a tail, it can also measure the wing-to-stab distance.

Camera access is off: Tap Open Settings and turn on Camera for Maiden.
Camera measuring isn't available: This iPhone can't track its position. Measure the wing from a photo instead.

Span: The width of the wing from tip to tip. Half-span is one side, from the centerline to the tip.
Tip: The outer end of a wing or stab.