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PMP lesson · Quality · Quality · lesson 3 of 3 · about 7 minutes

The quality tools: which one, when?

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Goal: After this lesson you can pick the right quality tool from the question being asked, and read a Pareto chart.

1The situation

The gripper keeps dropping parts

During the robot cell's first production week, the gripper drops parts several times a shift. Everyone has a theory: worn suction cups, oily parts, low air pressure, a changed teach point.

You need to do three things: list all possible causes systematically, find out which problems happen most often, and check whether one factor really drives the defects.

Each of those questions has its own quality tool.

2Match the tool to the question

The exam rarely asks you to draw a tool. It asks you to choose the right one from the situation. Start from the question:

If the question is about…Choose
finding causes of a problemCause-and-effect (fishbone) diagram, 5 whys
ranking problems by frequency (“fix the vital few”)Pareto chart
the relationship between two variablesScatter diagram
process stability over timeControl chart
collecting data on the spotCheck sheet
the distribution of valuesHistogram
the steps of a processFlowchart
Key words: “root cause” → fishbone · “most frequent”, “80/20” → Pareto · “correlation”, “relationship” → scatter · “stable”, “over time” → control chart.

3A fishbone for the gripper

Gripper dropsparts MachineMethodMaterialMeasurementMan (people)Environment worn suction cupspick speed too highoily part surfacevacuum sensor driftteach point changedlow air pressure
The six “M” categories help the team list causes systematically before choosing what to test.

4How it looks on the exam

Exam-style question 1. The quality engineer suspects that ambient temperature affects the rate of adhesive defects and has recorded both values for sixty shifts. Which tool should be used to examine the relationship?
A. Pareto chart
B. Cause-and-effect diagram
C. Scatter diagram
D. Check sheet
Show the answer and the decode
Answer: C.
In simple English
Two measured variables; is there a link?
What is the question really asking?
The right tool.
Key words / trigger
“temperature … rate of adhesive defects”
PMP logic
A scatter diagram plots two variables to show correlation.
Why the wrong answer looks attractive
A fishbone lists possible causes but does not test them with data.

5Remember this

Your memory card

  • Fishbone / 5 whys = possible causes · Pareto = most frequent (80/20)
  • Scatter = relationship · Control chart = stability over time
  • Check sheet = collect data · Histogram = distribution · Flowchart = process steps
  • Choose the tool from the question, not from habit
The full lesson in the PMCLEAR app also has:
  • the rest of the lesson (The Pareto principle)
  • a worked example
  • the common traps (wrong vs right)
  • 2 exam-style questions with the decode
  • a 3-question quick check
  • an interactive calculator
Open the full lesson → Create a free account
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