Compare one change

Example

Return to the same table-mounted arm. Trial A uses our target (20, 0, 15) cm and the 1 cm success rule. A controller is the program that chooses how the arm moves.

The following fictional results are supplied for this exercise. You do not need to run a simulation.

Trial	Target height	Controller	Final distance from target
A	15 cm	Original program	2 cm
B	17 cm	Different program	0.5 cm

In both trials, X = 20 cm and Y = 0 cm, the arm starts in the same position, and the success rule stays within 1 cm.

Your turn

Write or choose your answers before checking:

1. Which trials meet the success rule: A, B, both or neither?

2. Name the two things that changed from A to B.

3. Can these results show that raising the target caused the improvement?

4. You want to investigate height alone. Choose a fair comparison with A: C: height 17 cm, original program, same starting position and success rule. Or D: height 17 cm, different program, same starting position and success rule.

5. Before looking at the explanation, predict whether C will succeed, fail, or remain uncertain. What measurement would you need to check your prediction?

Check your reasoning

1. B only. Its 0.5 cm error is within 1 cm. A’s 2 cm error is outside it.

2. Target height and controller. Both changed, so the improvement could relate to either change or their combination.

3. No. These two trials do not isolate the effect of height.

4. C. Compare A and C with only target height changed. Keep the controller, X and Y, starting position and success rule fixed.

5. Any of those predictions is a starting hypothesis, not an established result. C has not been run and no result is supplied. Measure its final distance from its target, then compare that distance with the 1 cm rule. Record both your prediction and the outcome, even if they disagree.

You have designed a comparison that isolates one change. Repeated trials would still be needed to assess consistency. Fictional examples and simulated results do not establish how a physical robot will perform.

Ready to apply the three lessons? Choose your next step.