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Grade 9 · Science

Check measurement evidence before a design decision

Recognize how calibration, repeatability and test conditions affect a prototype comparison.

6 authored questions + worked example

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Worked example

A force sensor reads 0.4 N when no force is applied.

What is the best next step for this engineering comparison?

Answer & why

Answer: Check and correct the zero offset before comparing forces.

A nonzero unloaded reading suggests an offset that could affect comparisons.

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All questions

All 6 authored questions for this skill.

Question 1

A distance sensor is tested at known distances of 10, 20 and 30 cm.

What is the best next step for this engineering comparison?

  1. Compare its readings with all three known distances.
  2. Assume one accurate point proves accuracy at every distance.
  3. Test only at an unknown distance.
  4. Check only its casing color.
A hint

Check the measurement system and competing explanations before judging the design.

Answer & why

Answer: Compare its readings with all three known distances.

Several reference values help show how the sensor behaves across the tested range.

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Question 2

A team compares two water-level alarms, but one test uses a tilted tank.

What is the best next step for this engineering comparison?

  1. Level the tank and repeat the comparison under matching conditions.
  2. Record only the loudest alarm name.
  3. Change the tank and alarm at the same time again.
  4. Credit all differences to the alarms.
A hint

Check the measurement system and competing explanations before judging the design.

Answer & why

Answer: Level the tank and repeat the comparison under matching conditions.

Tank tilt is a competing explanation, so the comparison should control it.

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Question 3

A scale repeatedly reports a known 100 g mass as 105 g.

What is the best next step for this engineering comparison?

  1. Investigate calibration before using it to compare designs with small mass differences.
  2. Ignore all repeat measurements.
  3. Treat a 1 g difference as certainly meaningful.
  4. Conclude the reference mass gained 5 g without more evidence.
A hint

Check the measurement system and competing explanations before judging the design.

Answer & why

Answer: Investigate calibration before using it to compare designs with small mass differences.

A repeatable discrepancy from a reference can bias a design decision.

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Question 4

A light sensor gives very different readings when the same lamp setup is repeated.

What is the best next step for this engineering comparison?

  1. Claim one trial identifies a permanent winner.
  2. Investigate the measurement variation and repeat tests before choosing a design.
  3. Use only the most favorable reading.
  4. Hide the measurements that disagree.
A hint

Check the measurement system and competing explanations before judging the design.

Answer & why

Answer: Investigate the measurement variation and repeat tests before choosing a design.

Variable measurements make a design comparison less secure until the variation is understood.

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Question 5

A force sensor reads 0.4 N when no force is applied.

What is the best next step for this engineering comparison?

  1. Check and correct the zero offset before comparing forces.
  2. Change the design without checking the sensor.
  3. Treat every small force as exactly correct.
  4. Delete the readings without investigating.
A hint

Check the measurement system and competing explanations before judging the design.

Answer & why

Answer: Check and correct the zero offset before comparing forces.

A nonzero unloaded reading suggests an offset that could affect comparisons.

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Question 6

Two temperature sensors in the same steady sample disagree by 3°C.

What is the best next step for this engineering comparison?

  1. Assume the warmer reading always belongs to the better design.
  2. Compare them with a suitable reference before attributing the difference to the designs.
  3. Average them and declare the disagreement impossible.
  4. Claim both designs certainly have different temperatures.
A hint

Check the measurement system and competing explanations before judging the design.

Answer & why

Answer: Compare them with a suitable reference before attributing the difference to the designs.

The difference could come from measurement rather than the designs.

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