Lesson 6 · Two-Sensor Line Following — Knowledge ChecksAnswer key

The left sensor reads 0.8 and the right reads 0.2. What is the error, and which way has the robot drifted?

1. A.error +0.6, drifted left✓
2. B.error −0.6, drifted right
3. C.error 0.0, centered
4. D.error 1.0, at an intersection

error = 0.8 − 0.2 = +0.6. A positive error means the left sensor is on the line, so the robot drifted left.

Why is the correction negated in arcade(base_effort, -correction) here, when Lesson 5 didn't negate it?

1. A.The meaning of a positive error flipped, so the steer direction has to flip too✓
2. B.Two sensors always need a negative sign no matter what
3. C.It makes the robot go faster
4. D.It fixes a bug in arcade()

With two sensors, a positive error means 'drifted left → steer left', which is a negative turn in arcade — so we negate the correction.

Both sensors suddenly read high (0.9 and 0.9), so error ≈ 0 and the robot drives straight. What has it most likely reached?

1. A.The edge of the table
2. B.An intersection — a second line crossing the first✓
3. C.A dead battery
4. D.The end of the program

Both sensors on black at once usually means a crossing line. The two-sensor follower can't tell that apart from 'centered' — which is exactly the problem Lesson 7 solves.