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Before you measure

A minute here saves a wasted lap.

Safety first

Firm, level ground; engine off; parking brake on; wheels chocked.
Never get under, or reach under, a car held up only by a jack. Use rated jack stands. For measuring, the car stays on its wheels: don’t jack it up.
Take the phone and the bracket off before the car moves. Never use the app while driving.

Adjusting? See the safety rules in Adjust toe safely.

The car

Ground as level as you can find. Remove unusually heavy cargo.
Steering wheel centered: spokes level and the logo upright, the way it sits when you drive straight. Go by the steering wheel, not the tires.
Roll forward a few feet in a straight line and stop without touching the brake, so the suspension settles. Then engine off, parking brake on, and chock the wheels.
Don’t touch the steering wheel again until the lap is done.
Set the tire pressures as you normally run them.

Wheel covers off.
Wipe the flat ring at the top of each rim’s lip, where the prongs will sit. Avoid the valve stem and clip-on weights.
Never measure off the tire or the hub. The prongs go on the metal lip only.

All windows fully up and doors shut firmly. Nobody in or leaning on the car. For thrust angle, see its own checklist.

Let the phone get used to the air for 3 to 5 minutes with the app open, longer going from a warm pocket into the cold or from air conditioning into heat. A phone that is warming up or cooling down drifts, and the lap may not close.
Phone clamped in the bracket, screen up. FRONT will point toward the front of the car at every wheel.
Calibration current: within 30 days, with this phone and this bracket.
Turn up the media volume, so you hear when a reading is taken.

The app shows a short version of this list, How to Get Better Readings, the first time you start a lap, and any time behind the ? button.