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Continuous Improvement Toolkit
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Free Lean Six Sigma toolkit

Run your next DMAIC project in your browser.

Nine guided tools, six reference guides and 21 printable cheat sheets for practitioners at every belt level. No sign-up. Your work saves in this browser as you go, and you can save a project file to keep or share.

New to Lean Six Sigma? Read the overview

Work through DMAIC

Pick the phase your project is in. Each phase lists its tools and the guides behind them.

Define

Agree the problem, goal and scope.

Tools
Guides

Measure

Establish a reliable baseline.

Tools
Guides

Analyse

Find and verify the root causes.

Tools
Guides

Improve

Test and implement countermeasures.

Tools
Guides

Control

Sustain the gain and hand over to the process owner.

Tools
Guides

Across every phase

Tools that run the length of the project. Keep the A3 current at every tollgate and capture lessons as you go, not only at close.

Define Phase · Tool 1

Project Charter

The formal authorisation document for your project. Defines scope, goals, team and timeline to get everyone aligned before improvement work begins.

Why start with a Charter?

The charter prevents the most common project failure mode: starting without alignment. It answers three questions. What exactly are we fixing? (problem statement). How will we know we've succeeded? (SMART goal and metrics). What is and isn't included? (scope). If the Sponsor won't sign it, the project isn't ready to start.

1
Problem Statement
What, where, since when, how big?
2
Business Case
Why does this matter to the organisation?
3
Goal Statement (SMART)
Specific, Measurable, Achievable, Relevant, Time-bound
4
Key Metrics
How will we measure success?
Metric (Y)BaselineTargetUnit
5
Project Scope
Define the boundaries clearly
In Scope
Out of Scope
6
Project Team
Team Members
7
High-Level Timeline
PhaseMilestoneTarget DateOwner
8
Risks, Assumptions & Dependencies
9
Sign-off
Charter is not active until signed by all parties
Sponsor
Champion
Belt
Define Phase · Tool 2

SIPOC Diagram

Map each process step with its linked suppliers, inputs, outputs and customers. Work from the Process column outward for best results.

How to complete this SIPOC

1. Start with Process steps and define 4 to 7 high-level steps using verb + noun format (e.g. "Receive request"). 2. For each step, add the Inputs required and the Outputs it produces. 3. Then identify Suppliers who provide those inputs and Customers who receive the outputs. Each row represents one step and its directly linked elements.

Suppliers
Who provides inputs?
Inputs
What goes in?
Process Step
Verb + noun
Outputs
What is produced?
Customers
Who receives outputs?
Guidance & Common Mistakes
Suppliers
Think broadly. Internal teams, external vendors, regulatory bodies and automated systems all count. A team can be both supplier and customer.
Inputs
Inputs are what's needed to run the step. Think data, forms, approvals and materials. What would stop this step from starting if it was missing?
Process Steps
Use verb + noun format. Aim for 4 to 7 steps. Each should represent a meaningful transformation and avoid swimlane-level detail.
Outputs
Outputs are what the step produces, not activities. Each output should trace to at least one customer in the same row.
Customers
Customers can be internal (next team in the process) or external (end users, regulators). Understanding their needs shapes what a good output looks like.
Common Mistakes
Too much detail. Confusing inputs with outputs. Missing internal customers. Listing activities as outputs. Starting with Suppliers instead of the Process column.
Analyse Phase · Tool 3

5 Whys

Iteratively ask "Why?" to move from symptom to root cause. Each problem gets its own collapsible chain and you can extend beyond 5 when needed. The number is a guide, not a rule.

No problems added yet. Click "+ New Problem" to start a 5 Whys chain.
Tips for effective 5 Whys
→Ask "why the process allows this" not "who did this." Focus on systems, not blame.
→Each answer should logically lead to the next why. Test the chain by reading it bottom-up.
→Stop when you reach a cause you can actually change. It may take 3 whys or it may take 7.
→Validate the root cause. If you fix it, does the problem go away permanently?
Analyse Phase · Tool 4

Fishbone Diagram

Visual cause and effect analysis. Enter your problem, add causes by category and the diagram updates live. Category labels are editable.

Causes by Category

Facilitation Tips

Start with a clear problem statement before the team assembles. During the session, work through one category at a time with a 2-minute silent sticky note round followed by a share-out. Defer judgement during the brainstorm, then use dot voting to identify the 2 or 3 most likely root causes. Investigate each selected cause with 5 Whys. See the Cheat Sheets page for the full Fishbone Facilitation Guide.

Across every phase · Tool 5

A3 Report

Tell the complete improvement story on a single structured page. The A3 format was pioneered by Toyota and forces real clarity. If it doesn't fit on one page, the thinking isn't ready yet.

1
Background / Business Case
Why does this matter?
2
Current Condition
Where are we now?
3
Goal / Target Condition
Where do we want to be?
4
Root Cause Analysis
Why is it happening?
5
Countermeasures / Solutions
What will we do about it?
6
Implementation Plan
Who does what by when?
ActionOwnerDue DateStatusNotes
7
Results & Confirmation
Did it work?
8
Follow-up & Standardisation
How do we sustain it?
Improve and Control · Tool 6

FMEA Analysis

Failure Mode and Effects Analysis. Identify what could fail and prioritise risks using RPN = Severity × Occurrence × Detection.

How to use FMEA

For each process step, identify potential failure modes. For each, describe its effect, then rate Severity (S), Occurrence (O) and Detection (D) on a 1 to 10 scale. The RPN (S × O × D) tells you where to focus. Address high-RPN items first, especially where Severity is 8 or above.

RPN Priority Guide
≥200 Critical. Act immediately.
100–199 High. Plan action now.
50–99 Medium. Monitor closely.
<50 Low. Document and review.
Scale: 1 = Very low · 5 = Moderate · 10 = Very high
Process StepFailure ModeEffectRiskRPNCauseControlsRecommended ActionOwnerNew RPN
SOD
Enter 1–10 for S, O, D. RPN calculates automatically.

Lessons Learnt

Reference Library

Cheat Sheets

21 print-ready reference cards covering every tool and DMAIC phase. Click any card to preview and print as PDF.

DMAIC Phase Guides
Tool Reference Cards
Learn & Workshop Guides

What is Lean Six Sigma?

A complete guide to the methodology, its origins, the 5 Lean principles, belt structure, and how DMAIC drives lasting improvement.

The Origins

Lean originated in the Toyota Production System (TPS) in post-war Japan, pioneered by Taiichi Ohno and Shigeo Shingo. Its core insight: the only work worth doing is work the customer would pay for. Everything else is waste.

Six Sigma was developed at Motorola in the 1980s and popularised by General Electric under Jack Welch in the 1990s. It uses statistical methods to reduce process variation, targeting fewer than 3.4 defects per million opportunities.

Lean Six Sigma combines both: Lean's speed and waste elimination with Six Sigma's rigour and defect reduction. Together they are more powerful than either alone.

The 5 Lean Principles

1
Define Value from the customer's perspective. If the customer wouldn't pay for it, it's likely waste.
2
Map the Value Stream by identifying every step. Classify each as value-adding, necessary non-value-adding or pure waste.
3
Create Flow by removing barriers so work moves smoothly without stops, queues or rework.
4
Establish Pull by producing only what the customer needs, when they need it. Overproduction is waste.
5
Pursue Perfection. Improvement never stops. Small continuous improvements compound significantly over time.

The Belt Structure

White / Yellow Belt
Awareness level. Understands LSS concepts, participates as a team member. Typically 1–3 days training.
Green Belt
Part-time project lead. Leads smaller projects, supports Black Belt on complex ones. Proficient in all DMAIC tools.
Black Belt
Full-time improvement expert. Leads complex projects, mentors Green Belts, expert in statistical analysis.
Master Black Belt
Strategic programme leader. Coaches BBs, selects projects, drives culture change, owns LSS deployment.

Process Mapping

A guide to all common process mapping styles, from high-level SIPOC to detailed swimlane maps and value stream maps. Choose the right tool for the right question.

Why Map Processes?

You cannot improve what you cannot see. Process mapping creates a shared understanding of how work actually flows versus how people think it flows. It surfaces waste, handoffs, delays and rework loops, and gives you the baseline from which improvement is measured.

Key principle: Always map the current state first. Resist designing the future state before you truly understand where waste exists today. Walk the process and observe it in person rather than drawing from memory in a meeting room.

SIPOC

High-level 5-column view. 4–7 process steps. Used in Define phase to scope the project and align stakeholders on boundaries. Start here before any detailed mapping.

Best used when

Starting a project, aligning a team on scope, communicating to senior stakeholders.

Standard Flowchart

Sequential steps as boxes and diamonds (decisions). Shows logical flow including decision branches, loops, and endpoints. Good for documenting procedures and standard work.

Best used when

Documenting a procedure, identifying decision points, creating standard work instructions.

Swimlane / Cross-Functional

Flowchart organised by lane (person, team, or system). Handoffs become immediately visible, which is a key source of waiting and errors. The most powerful map for identifying where delays occur.

Best used when

Multiple departments involved; when you need to surface handoff delays and ownership gaps.

Value Stream Map (VSM)

Shows material and information flow from supplier to customer. Includes cycle time, wait time, inventory levels. Distinguishes value-adding from non-value-adding time. See the VSM page for detail.

Best used when

Measure phase. Use it for calculating total lead time, identifying bottlenecks and inventory buffers.

Spaghetti Diagram

Tracks physical movement of a person, product, or information through a space. Drawn on a layout map. The tangled lines ("spaghetti") reveal unnecessary motion and transport waste.

Best used when

Physical layout is suspected as a waste source, particularly in manufacturing or service environments.

Deployment / Matrix Map

Maps responsibilities against process steps in a grid (rows = roles, columns = steps). Shows RACI-style involvement at each stage. Identifies over/under-involvement of teams.

Best used when

Clarifying roles across a complex process; preparing standard work; RACI alignment.

Standard Flowchart Symbols

PROCESS
Rectangle
A process step or activity
YES/NO?
Diamond
A decision point
START
Oval
Start or end point
Document
A document or report
Parallelogram
Input or output / data
Dashed box
Sub-process (detail elsewhere)

Value Stream Mapping

VSM is the most powerful tool for seeing and eliminating waste across an entire process, from customer demand back to the first input.

What is a Value Stream Map?

A VSM shows the complete flow of materials and information required to bring a product or service to a customer. Unlike standard process maps, VSM captures time data including cycle time, wait time and total lead time, making waste visible in a way that flowcharts simply cannot.

The golden ratio: In most processes, value-adding time represents less than 5% of total lead time. The rest is waiting, batching, inspection and transport. VSM makes this gap undeniable and measurable.

How to Build a Current State VSM

1
Define the product family by selecting the group of products or services that follow a similar path.
2
Walk the process. Go where work happens, observe and time each step directly. Do not map from memory.
3
Draw from right to left, starting with customer demand and tracing backwards to the supplier or input.
4
Capture data boxes under each process box. Record Cycle Time (CT), Change-over Time (C/O), uptime (%), number of operators and batch size.
5
Add inventory triangles between each step and record the quantity of items waiting.
6
Draw the timeline with value-adding time below the line and wait time above. Sum both to get total lead time.

Key VSM Metrics

Cycle Time (CT)

Time to complete one unit at a single step. Measured directly at the process.

Lead Time (LT)

Total time from start to finish, including all waiting. This is what the customer actually experiences.

Takt Time

Available time ÷ Customer demand rate. The heartbeat of the process and how fast you must produce to meet demand.

Process Cycle Efficiency (PCE)

Value-Adding Time ÷ Total Lead Time × 100%. World class: >25%. Most start at 1–5%.

Data Gathering

The Measure phase lives or dies on data quality. Key tools for collecting reliable, representative data that tells the truth about your process.

The Measurement Philosophy

Before collecting data, answer three questions: What exactly are we measuring? (operational definition), How will we collect it? (sampling strategy), and How will we verify the measurement system is reliable? (Gage R&R). Poor data produces false root causes and wrong solutions.

Warning: "We already have the data" is the most dangerous phrase in a Measure phase. Historical data often has gaps, inconsistent definitions and unknown collection biases. Always validate before using it.

Check Sheet

A pre-designed form for tallying defects, issues, or events by category and time. Reduces transcription error. The simplest and most reliable data collection tool.

Design tips

Columns = categories (defect types). Rows = time periods or locations. One tick = one occurrence. Include who, when, where fields.

Observation Sheet

Records what actually happens during direct observation. Captures cycle times, wait times, motion, and deviations from standard work. Never rely on self-reporting alone.

Key fields

Step name, start time, end time, cycle time, issues observed, operator, date/shift, notes column.

Stratification

Collect data broken down by the factors most likely to cause variation: shift, machine, operator, supplier, day of week, location. Averaging across strata hides the real source of variation.

Why it matters

"Average defect rate 4%" hides "Machine 3 night shift has 18% defect rate."

Sampling Strategy

You rarely need 100% of data. Choose an approach that gives reliable conclusions without excessive effort.

  • Random: every item has equal chance of selection, which minimises bias
  • Systematic: every nth item, practical for high volume processes
  • Stratified: random within subgroups, ensures all strata are represented
  • Subgroup: small samples at regular intervals, used for control charts

Voice of the Customer (VOC)

Structured methods for capturing what customers actually need:

  • Interviews are open-ended, one-to-one and produce the richest data
  • Surveys have wider reach and produce quantifiable results
  • Complaints and escalations represent already-captured customer pain
  • Focus groups allow shared issues to surface through discussion
  • Observation involves watching customers use the process directly
VOC → CTQ: Translate customer statements into Critical to Quality characteristics that are measurable and specific.

Gage R&R (MSA)

Determines how much variation in your data comes from the measurement system itself.

Repeatability

Same person, same part, same equipment. Does it give the same reading?

Reproducibility

Different people measuring the same thing. Do they get the same reading?

Rule of thumb: %GRR <10% = acceptable. 10–30% = marginal. >30% = fix the measurement system before collecting data.

Data Analysis

Turning collected data into insights that point to root causes and guide improvement decisions. Covers Pareto, control charts, capability, and supporting tools.

Pareto Analysis: The 80/20 Principle

Typically 80% of defects come from 20% of causes. Pareto analysis helps you focus effort where it will have the greatest impact. Always stratify data before building a Pareto chart. Pooling data from different shifts, machines or teams hides the real pattern.

How to Build a Pareto Chart

1
Collect and categorise. Count frequency or cost by category such as defect type, failure mode or complaint reason.
2
Sort descending, ranking from most frequent or costly to least.
3
Calculate cumulative % as a running total of percentage of total. This becomes your line on the secondary axis.
4
Draw the chart with bars in descending order and the cumulative % line overlaid. Mark the 80% threshold.
5
Identify the vital few. Categories to the left of where the line crosses 80% are your priorities. Investigate these with 5 Whys.
Example: Invoice Error Causes
Wrong
code
42%
Missing
field
27%
Wrong
supplier
14%
Dupli-
cate
7%
Other
5%
Defect category
Cumulative %
Wrong code42%
+ Missing field69%
+ Wrong supplier83% ← 80th
+ Duplicate90%
+ Other100%
Vital few: Fix first 3 causes → eliminate 83% of all errors.
Stratify before you Pareto: Run separate charts for each shift, location or team. Pooling data hides the real pattern and leads to the wrong conclusion.

Control Charts: The Voice of the Process

A control chart is a run chart with statistically derived upper and lower control limits (UCL/LCL). Its purpose is to distinguish common cause variation (random noise inherent to the process) from special cause variation (something unusual that warrants investigation). Only special causes should be investigated. Tampering with common cause variation makes things worse.

Choosing the Right Chart

Data TypeSubgroup = 1Subgroup 2–9Subgroup ≥10
Continuous (variable)XmR / ImRXbarRXbarS
Defective (pass/fail)—p-chart (variable n) · np-chart (fixed n)
Defects (count)—c-chart (fixed area) · u-chart (variable area)

XmR Control Limit Formulas

X̄ = Sum of all values ÷ n
mR̄ = Average |Xi – Xi-1|
UCL(X) = X̄ + 2.66 × mR̄
LCL(X) = X̄ − 2.66 × mR̄
UCL(mR) = 3.27 × mR̄

Constants 2.66 and 3.27 derived from d2 and D4 for n=2 subgroups.

The Nelson Rules: Signals of Special Cause

Any single rule violation warrants investigation. These rules detect patterns statistically unlikely under common cause variation.

Rule 1: Beyond 3σ

1 point outside UCL or LCL. Probability 0.27%. Most obvious special cause signal.

Rule 2: Nine in a Row

9 consecutive points on the same side of the centreline. Suggests a sustained shift in the process mean.

Rule 3: Six Trending

6 consecutive points continuously increasing or decreasing. Suggests gradual drift such as tool wear, degradation or seasonal effect.

Rule 4: Fourteen Alternating

14 points alternating up-down. Suggests two alternating processes (two machines, two operators).

Rule 5: Two of Three Near Limits

2 of 3 consecutive points beyond 2σ on the same side. Early warning of a shift.

Rule 6: Four of Five Beyond 1σ

4 of 5 consecutive points beyond 1σ from centreline on the same side.

Rule 7: Fifteen Within 1σ

15 points within 1σ of centreline. Suggests stratification and that data may be from mixed processes.

Rule 8: Eight on Both Sides

8 consecutive points on both sides, none within 1σ. Suggests a bimodal distribution from two mixed processes.

Process Capability: Cp and Cpk

Cp: Potential Capability
Cp = (USL − LSL) / (6σ)

Measures how well the process spread fits within specification limits, assuming it is perfectly centred. It ignores any off-centring.

Cpk: Actual Capability
Cpk = min[(X̄−LSL)÷3σ, (USL−X̄)÷3σ]

Measures actual performance and accounts for off-centring. When Cpk is lower than Cp the process is not centred on target.

Cpk <1.0: Produces defects. Not capable.
Cpk 1.0–1.33: Marginally capable. Any shift creates defects.
Cpk >1.33: Capable. World class target: Cpk ≥ 1.67.

Other Key Analysis Tools

Histogram

Shows the distribution of continuous data including shape (normal, skewed, bimodal), spread and whether data falls within specification. Always look at shape before using mean/SD. A bimodal histogram suggests two mixed processes.

Scatter Diagram

Plots two variables to explore correlation (X vs Y). Does not prove causation, but a strong correlation is worth investigating. Look for direction (positive/negative), strength, and outliers. Used to validate suspected X → Y relationships.

Box Plot

Shows median, interquartile range, and outliers. Excellent for comparing distributions across groups (shifts, machines, operators). A box plot comparison is almost always more informative than comparing means alone.

The 8 Wastes: TIMWOODS

Originally 7 wastes from the Toyota Production System, expanded to 8 with Non-utilised Talent (Skills). Every waste consumes resources without adding value the customer would pay for. Learning to see waste is the first step to eliminating it.

What Is Waste?

In Lean thinking, work falls into three categories. Value-Adding (VA) covers activities the customer would pay for if they understood them. Necessary Non-Value-Adding (NNVA) covers activities required by the current system but not valued by the customer, such as regulatory compliance or system limitations. Pure Waste (NVA) covers activities that can and should be eliminated immediately.

Taiichi Ohno: "All we are doing is looking at the timeline from the moment the customer gives us an order to the point when we collect the cash. And we are reducing that timeline by removing the non-value-adding wastes." The 8 Wastes framework is the lens for finding them.
The 8 Wastes in Detail
T
Transport

Unnecessary movement of materials, products, information, or people between locations.

Examples

Moving files between shared drives · Sending documents between departments for sequential review · Physical movement of goods to interim storage before final destination

Ask yourself

Does this item need to travel this far? Can the next step be co-located? Can we remove the handoff entirely?

I
Inventory

Excess stock, work-in-progress, or information queuing beyond what is immediately needed.

Examples

Emails sitting unread in shared inboxes · Partially completed work batched before the next step · Spare parts stockpiled beyond safety stock levels

Ask yourself

Why is this waiting? What is causing the build-up? Can we reduce batch sizes or implement pull?

M
Motion

Unnecessary movement by people. Walking, reaching and searching for tools, information or equipment.

Examples

Searching for files across multiple systems · Walking to a printer across the office · Switching between applications to complete a single task

Ask yourself

Is everything needed within easy reach? Can layout or system design reduce searching and switching?

W
Waiting

Idle time when people, equipment, or information is delayed between process steps.

Examples

Waiting for approvals or sign-offs · System downtime · Waiting for a meeting to start · Dependencies on another team's deliverable

Ask yourself

What is the person or process waiting for? Is this a capacity issue, a policy issue, or a communication failure?

O
Overproduction

Producing more than needed, sooner than needed, or faster than the customer requires. Often considered the worst waste as it creates or hides all others.

Examples

Reports produced but never read · Preparing more stock than can be sold · Sending notifications to people who don't need them

Ask yourself

Does anyone actually use this? Are we producing based on demand or just "in case"?

O
Over-processing

Doing more work, adding more features, or applying more quality than the customer actually values or requires.

Examples

Reformatting reports into multiple templates · Multiple approval layers for low-risk decisions · Polishing a document that will only be read once

Ask yourself

Is this step explicitly required by the customer? Would removing it be noticed?

D
Defects

Errors, mistakes, or non-conformances requiring rework, correction, scrapping, or customer complaint handling.

Examples

Incorrect invoices requiring reissue · Data entry errors causing downstream rework · Software bugs requiring patches · Mis-shipped orders

Ask yourself

What causes this error? Is there a poka-yoke (mistake-proofing) solution? Why wasn't it caught earlier?

S
Skills (Non-utilised Talent)

Failing to use the knowledge, creativity, skills, and experience of people in your organisation. The "8th waste" added when Lean expanded beyond manufacturing.

Examples

Not involving front-line staff in improvement decisions · Qualified staff doing tasks below their capability · Ignoring improvement ideas from operators

Ask yourself

Are we listening to the people closest to the work? Are skills being used to their full potential?

How to Use This Framework

In a Gemba Walk

Walk the process with fresh eyes. For each step, ask which of the 8 wastes is present. Use a tally sheet to count occurrences by type. A Pareto of waste types will tell you where to focus.

In a VSM Session

As you build your current-state Value Stream Map, mark each non-value-adding step with its waste type. This connects the 8 Wastes framework directly to your improvement priorities.

In a DMAIC Project

Use TIMWOODS in the Analyse phase to classify root causes. Most root causes trace back to one or more waste types and naming them helps teams prioritise countermeasures in the Improve phase.

Common mistake: Jumping straight to eliminating waste without understanding why it exists. Waste is usually a symptom of a process, system, or policy problem. Use 5 Whys to find the root cause before redesigning.
Measure Phase · Tool 8

Data Collection Plan

Decide what to measure, exactly how, how much and by whom before anyone collects a single number. A clear plan is the difference between a baseline the team trusts and one it argues about.

Plan before you collect

Start with the project Y from your Charter, then add the Xs you suspect drive it. For each, write an operational definition precise enough that two people measuring the same item get the same answer. Decide how much data you need and what to record alongside it (shift, site, product type) so you can stratify later. Then check the measurement system before you trust the numbers.

MeasureY or XData typeOperational definitionSource and locationSample size and frequencyWho collectsStratify by
One row per measure. Put the project Y first.
Measurement system check
Guidance & Common Mistakes
Operational definitions
"Invoice processing time" is a name, not a definition. "Calendar days from the date stamp in the AP inbox to the payment date in the finance system, excluding invoices on hold for a dispute" is. State where the clock starts and stops, the unit, and what is excluded.
Continuous or discrete
Continuous data (time, cost, weight) tells you far more per data point than pass/fail or counts. Where you can, measure the continuous thing behind the defect, such as days late rather than late or on time.
How much data
Rules of thumb: for continuous data, at least 30 values spread across normal conditions. For pass/fail data, enough items to see at least 5 defects in every group you want to compare. For a run chart, 20 or more points over time.
Stratify from the start
Record the factors you might want to slice by (shift, site, product, customer type) at the moment of collection. Adding them afterwards is usually impossible, and stratification is often where the root cause shows itself.
Common mistakes
Collecting what is easy rather than what answers the question · No operational definitions · Skipping the measurement system check · Changing the process while you baseline it · No one owns the collection.
Next step
Plot the project Y over time on a Run Chart. If the baseline shows shifts or trends, find out why before you move on to Analyse.
Measure and Control · Tool 9

Run Chart

Plot your measure over time against its median. Simple rules tell you whether you are looking at a real change or ordinary variation, with no statistics software needed.

How to read a run chart

Collect at least 10 points before reading signals, and 20 or more for a solid baseline. Points that sit exactly on the median are ignored by the rules. Three rules are checked for you: a shift (6 or more points in a row on one side of the median), a trend (5 or more points in a row all going up or all going down) and too few or too many runs. Check a fourth by eye: an astronomical point, a value so different that everyone would agree it is unusual.

Data
#Label or dateValue
Paste a column from a spreadsheet
Guidance
Why the median
The median is not dragged around by one extreme value, and the run rules are built on it: by chance, half the points should fall on each side. That is why the chart uses the median, not the mean.
Baseline, then freeze
Enter the number of baseline points to calculate the median from the period before your change only. The line is then extended (dashed), so new points are judged against the old median and a real improvement shows up as a shift.
A signal is a prompt
A signal says something changed, not what. Go and see. A shift in the improving direction straight after your countermeasure is good evidence that it worked. One in the wrong direction during Control means the gain is slipping.
Run chart or control chart
A run chart needs no assumptions about the data and works from 10 points. Once you have 20 or more and need to know whether the process is predictable, and within what limits, move to an XmR control chart (see the Data Analysis guide).