What is the walk-and-turn test and how is it scored?

It runs in two stages, and both are scored.

The instruction stage. You stand heel-to-toe with arms at your sides and listen without starting. Losing balance during instructions, or starting too soon, are two of the eight clues — before you've taken a step.

The walking stage. Nine heel-to-toe steps along an actual or imaginary line, counting aloud, watching your feet, arms down. A specific small-step turn. Nine steps back.

The eight clues: can't keep balance during instructions, starts too soon, stops while walking, doesn't touch heel to toe, steps off the line, uses arms for balance, turns improperly, wrong number of steps.

Two clues and the officer is trained to treat that as indicating impairment.

Consider how easily a sober person raises their arms on a sloped shoulder — that's one. Miss heel-to-toe by a half inch on one step — that's two.