Peak Flow is a health metric used in clinical and wellness assessments to support informed decision-making.

How is this calculated?

The calculation uses established medical formulas and evidence-based parameters to produce accurate results.

Who should use this calculator?

Healthcare professionals, students, and individuals seeking to understand their health metrics can benefit from this tool.

How accurate are the results?

Results are based on peer-reviewed formulas but should be verified with a healthcare provider for clinical decisions.

What inputs are needed?

The calculator requires specific health measurements which vary depending on the metric being calculated.

Can this replace medical advice?

No. This tool is for educational purposes and should not replace professional medical consultation.

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MEDICALPulmonaryHealth Calculator

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Peak Flow

Asthma well-controlled

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Evidence-based calculations Used in clinical settings worldwide Regular monitoring recommended

Ready to run the numbers?

Why: This calculation helps assess important health parameters for clinical and personal wellness tracking.

How: Enter your values above and the calculator will apply validated formulas to compute your results.

Evidence-based calculationsUsed in clinical settings worldwide

Sources:Medical LiteratureWHO Guidelines

Run the calculator when you are ready.

Understanding Peak FlowUse the calculator below to check your health metrics

Green Zone (80-100%)

Asthma well-controlled

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Yellow Zone (50-80%)

Caution - action needed

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Red Zone (<50%)

Emergency - immediate action

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COPD Patient

Chronic obstructive pattern

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Female Asthmatic

Well-controlled female patient

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Sample Scenarios

Green Zone (80-100%)

Asthma well-controlled

Yellow Zone (50-80%)

Caution - action needed

Red Zone (<50%)

Emergency - immediate action

COPD Patient

Chronic obstructive pattern

Female Asthmatic

Well-controlled female patient

Enter Peak Flow Data

Demographics

Age (years)

Gender

Height

Height Unit

Peak Flow

Measured PEFR (L/min)

Personal Best (L/min)

Clinical

Diagnosis

Current Symptoms

For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.

🏥 Health Facts

— WHO

— CDC

What is Peak Flow?

Peak Expiratory Flow Rate (PEFR) measures how fast you can blow air out of your lungs. It is a simple, portable test used to monitor asthma control. The "traffic light" zone system helps patients and providers assess asthma status and guide treatment decisions.

GREEN ZONE (80-100%)

Good control - all clear!

YELLOW ZONE (50-80%)

Caution - take action

RED ZONE (<50%)

Emergency!

Traffic Light Zone System

GREEN ZONE (80-100% of Personal Best)

• Asthma is under good control
• No symptoms or mild symptoms
• Continue regular controller medications
• Follow routine asthma action plan
• Normal activities can continue

YELLOW ZONE (50-80% of Personal Best)

• Asthma is getting worse
• Use rescue inhaler (quick-relief medication)
• May need to increase controller medications
• Contact healthcare provider if no improvement
• Identify and avoid triggers
• May need oral corticosteroids

RED ZONE (<50% of Personal Best)

• Medical emergency!
• Take rescue inhaler IMMEDIATELY
• Start oral corticosteroids if prescribed
• Seek emergency care if no improvement in 15-20 minutes
• Call 911 if in severe respiratory distress

Proper Peak Flow Technique

Stand up straight (if able)
Set the indicator to zero
Hold the meter horizontally
Take a deep breath as deep as possible
Place lips around mouthpiece forming tight seal
Blow out as HARD and FAST as possible (like blowing out candles)
Note the number where the marker stops
Reset and repeat 2 more times
Record the HIGHEST of the 3 readings

Common Technique Mistakes

• Coughing: Can falsely elevate or lower reading
• Leaky seal: Air escaping around mouthpiece
• Tongue blocking: Tongue obstructing airflow
• Not blowing hard enough: Need maximum effort
• Slow start: Must begin with forceful blast
• Only one attempt: Need best of 3

Establishing Personal Best

• When: During a period of good asthma control
• Duration: Measure morning and evening for 2-3 weeks
• After treatment: 15-20 minutes after bronchodilator
• Selection: Highest reading over the period
• Update: Reassess annually or after change in condition
• Better than predicted: Personal best is more accurate for monitoring

Normal Peak Flow Values

Age/Height	Males (L/min)	Females (L/min)
150 cm	390-450	300-360
160 cm	450-520	350-410
170 cm	510-590	390-450
180 cm	570-660	430-490
190 cm	630-730	470-530

Values decrease with age after ~25 years

Asthma Action Plan

• Written plan: Every patient should have a personalized plan
• Components: Daily management, how to handle worsening, emergency actions
• Peak flow: Use to guide zone-based actions
• Medications listed: Controller and rescue medications with doses
• Emergency contacts: Doctor, emergency room, 911
• Review regularly: At every asthma visit

When to Check Peak Flow

• Establishing personal best: Twice daily for 2-3 weeks
• Routine monitoring: Once daily (usually morning)
• During illness: More frequently when sick
• Before and after medications: Assess bronchodilator response
• With symptoms: Whenever experiencing asthma symptoms
• Environmental triggers: During allergy season, pollution events

Diurnal Variation

• Normal variation: PEFR typically highest in afternoon
• Morning dip: Lowest values usually on waking
• Normal range: <20% variation is normal
• Significant variation: >20% suggests poor control
• Calculation: (Evening - Morning) / Average × 100
• Clinical significance: High variability indicates labile airways

Bronchodilator Response

• Method: Check PEFR, give bronchodilator, recheck in 15-20 min
• Positive response: ≥20% improvement suggests reversible obstruction
• Asthma characteristic: Typically shows good bronchodilator response
• COPD: Usually less reversibility than asthma
• Clinical use: Helps confirm diagnosis, assess response to therapy

Peak Flow vs Spirometry

Feature	Peak Flow	Spirometry
Cost	Low ($15-30)	High
Portability	Pocket-sized	Office-based
Self-use	Yes	Needs technician
Parameters	PEFR only	FEV1, FVC, flows
Diagnosis	Monitoring	Diagnosis + monitoring

Choosing a Peak Flow Meter

• ATS/European standards: Look for EN 23747 compliance
• Range: 60-800 L/min covers most patients
• Low range: Available for children or severely limited patients
• Consistency: Use the same meter for serial measurements
• Maintenance: Clean weekly, replace per manufacturer guidelines

Clinical Pearls

• Personal best > predicted: Always use personal best when available
• Effort-dependent: Results depend on patient effort
• Large airway emphasis: PEFR reflects large airway function
• May miss small airway: FEF25-75 on spirometry more sensitive
• Falling PEFR: May precede symptoms by hours to days

Clinical Scenario Examples

Scenario 1: Well-Controlled Asthma

Personal best 550 L/min, morning reading 510 (93%). Green zone - continue current medications.

Scenario 2: Developing Exacerbation

Personal best 550 L/min, morning reading 380 (69%). Yellow zone - use rescue inhaler, increase controller, contact provider if no improvement.

Scenario 3: Severe Exacerbation

Personal best 550 L/min, reading 200 (36%). Red zone - use rescue inhaler immediately, seek emergency care.

Key Formulas

% Personal Best: (Measured / Personal Best) × 100
% Predicted: (Measured / Predicted) × 100
Diurnal Variation: (Evening - Morning) / Average × 100
Bronchodilator Response: (Post - Pre) / Pre × 100

Peak Flow Calculator Summary

GREEN

80-100%

All clear

YELLOW

50-80%

Caution

RED

<50%

Emergency

Documentation Guide

• Date and time: Record when measurement taken
• Value: Best of 3 attempts in L/min
• Personal best: Document and update
• Zone: Green, yellow, or red
• Symptoms: Any associated symptoms
• Actions taken: Medications used, provider contacted

Key References

Nunn & Gregg (1989)

New regression equations for predicting peak expiratory flow in adults. BMJ.

GINA Guidelines

Global Initiative for Asthma - management and prevention guidelines.

NAEPP Guidelines

National Asthma Education and Prevention Program - Expert Panel Report.

Memory Aids

• "Green means Go" - All clear, continue routine
• "Yellow means slow down" - Caution, take action
• "Red means STOP and get help" - Emergency
• "80-50 splits the zones" - 80% and 50% are the cutoffs
• "Best of 3" - Always record the highest reading

Key Takeaways

• Peak flow monitors airway obstruction simply and inexpensively
• Personal best is preferred over predicted values for monitoring
• Traffic light zones guide asthma management decisions
• Proper technique is essential for accurate results
• Daily monitoring can detect worsening before symptoms
• Every asthma patient should have a written action plan

Important Disclaimer

This calculator provides predicted peak flow values based on population equations. Individual variation is significant. Always establish a personal best when well-controlled. Peak flow should be used as part of a comprehensive asthma action plan developed with your healthcare provider. If in the red zone or experiencing severe symptoms, seek immediate medical attention.

Common Asthma Triggers

Allergens

• Dust mites
• Pet dander (cats, dogs)
• Pollen (trees, grass, weeds)
• Mold spores
• Cockroach particles

Irritants

• Tobacco smoke
• Air pollution
• Strong odors/perfumes
• Cleaning products
• Cold air

Exercise-Induced Bronchoconstriction

• Definition: Airway narrowing during or after exercise
• Peak flow drop: ≥15-20% from baseline
• Timing: Usually 5-20 minutes after starting exercise
• Prevention: Warm-up, pre-exercise bronchodilator
• Sports: Swimming often better tolerated (humid air)
• Peak flow use: Check before and after exercise

Occupational Asthma Monitoring

• Pattern: Symptoms worse at work, better on vacation/weekends
• Peak flow diary: Measure 4 times daily at work and off work
• Interpretation: >20% variation work vs off suggests occupational cause
• Common culprits: Isocyanates, flour, latex, wood dust
• Management: Remove from exposure if possible

Pediatric Peak Flow Considerations

• Age: Usually reliable from age 5-6 years
• Lower range meter: May be needed for small children
• Technique: May need extra coaching and practice
• Predicted values: Height-based equations used
• Personal best: Still important to establish
• Game approach: Can help with compliance

Elderly Patient Considerations

• Natural decline: PEFR decreases with age (~20 L/min per decade after 25)
• Physical limitations: Arthritis may affect grip and technique
• Comorbidities: May have both asthma and COPD
• Cognitive issues: May need caregiver assistance
• Personal best: Still the best comparator

Asthma During Pregnancy

• Rule of thirds: 1/3 improve, 1/3 same, 1/3 worsen
• Monitoring: More frequent peak flow monitoring recommended
• Medications: Continue controller medications - uncontrolled asthma more risky
• Goal: Maintain good control for maternal and fetal health
• Third trimester: Most likely time for exacerbation

Peak Flow in COPD

• Less variability: COPD shows less diurnal variation than asthma
• Less reversibility: Smaller bronchodilator response than asthma
• Chronic reduction: Persistently low PEFR
• Exacerbation detection: Can still help detect worsening
• Spirometry preferred: FEV1 is primary metric for COPD staging

Asthma-COPD Overlap (ACO)

• Features of both: Persistent obstruction with variability
• Peak flow: May show both fixed reduction and variability
• Bronchodilator response: Significant but incomplete
• Treatment: Usually requires both ICS and bronchodilators
• Monitoring: Peak flow still useful for exacerbation detection

Asthma Medications Overview

Quick-Relief (Rescue)

• Short-acting beta-agonists (SABA)
• Albuterol, levalbuterol
• Works in minutes
• Use for acute symptoms

Controller (Long-term)

• Inhaled corticosteroids (ICS)
• Long-acting beta-agonists (LABA)
• Leukotriene modifiers
• Daily use for prevention

Inhaler Technique Basics

• Shake: Shake inhaler before use (MDI)
• Exhale: Breathe out completely before inhaling
• Coordinate: Press inhaler at start of slow deep breath
• Hold: Hold breath for 10 seconds after inhaling
• Spacer: Use spacer for better delivery
• Rinse: Rinse mouth after ICS to prevent thrush

Common Questions

How often should I check peak flow?

Usually once daily when well-controlled. More often during illness or if symptoms develop. Check before and after rescue inhaler use.

Why is my peak flow lower in the morning?

Normal diurnal variation means peak flow is naturally lowest in early morning. Significant variation (>20%) may indicate poor control.

Should I use predicted or personal best?

Personal best is preferred once established. It accounts for your individual characteristics better than population-based predictions.

Step-by-Step Peak Flow Guide

Reset indicator to zero
Stand up straight
Take deepest possible breath
Place lips tightly around mouthpiece
Blow out as hard and fast as possible
Note the reading
Repeat twice more
Record the HIGHEST of 3 readings
Compare to personal best or predicted
Determine zone and follow action plan

Final Clinical Summary

Peak Expiratory Flow Rate (PEFR) is a simple, portable tool for monitoring airway obstruction. The traffic light zone system (Green 80-100%, Yellow 50-80%, Red <50%) provides an easy framework for patients to assess their status and take appropriate action. Personal best is preferred over predicted values for ongoing monitoring. Every asthma patient should have a written action plan.

GREEN

80-100%

YELLOW

50-80%

RED

<50%

Additional Resources

• Global Initiative for Asthma (GINA) - ginasthma.org
• American Lung Association - lung.org
• Asthma and Allergy Foundation - aafa.org
• National Heart, Lung, and Blood Institute - nhlbi.nih.gov
• American College of Allergy, Asthma & Immunology - acaai.org

Quick Reference Card

• GREEN ZONE: 80-100% personal best - all clear
• YELLOW ZONE: 50-80% personal best - caution
• RED ZONE: <50% personal best - emergency
• Best of 3: Record highest reading
• Personal best: Measure when well-controlled for 2-3 weeks
• Diurnal variation: >20% suggests poor control
• Bronchodilator response: ≥20% increase suggests reversibility

Viral Infections and Asthma

• Common trigger: Respiratory viruses are major asthma trigger
• RSV, rhinovirus: Particularly likely to trigger exacerbations
• Peak flow monitoring: Increase frequency during illness
• Early action: Start yellow zone treatment at first sign
• Recovery: May take 1-2 weeks for peak flow to normalize

Seasonal Considerations

• Spring: Tree pollen - allergic asthma may worsen
• Summer: Grass pollen, ozone, heat
• Fall: Weed pollen, mold, viral season begins
• Winter: Cold air, viral infections, indoor allergens
• Peak flow: May help predict seasonal patterns

Air Quality and Peak Flow

• AQI: Air Quality Index - check daily
• High AQI days: May see lower peak flow
• Ozone: Worse in summer afternoons
• Particle pollution: Wildfires, industry
• Action: Stay indoors on high pollution days

Asthma Emergency Preparedness

• Always carry: Rescue inhaler
• Know your zones: Memorize personal best and cutoffs
• Action plan: Written plan accessible at all times
• Emergency contacts: Doctor, ER, 911
• Medical ID: Consider wearing asthma identification
• Spacer: Keep with inhaler for better delivery

Biologic Therapies for Severe Asthma

• Omalizumab: Anti-IgE for allergic asthma
• Mepolizumab, Benralizumab: Anti-IL5 for eosinophilic asthma
• Dupilumab: Anti-IL4/IL13
• Indication: Severe uncontrolled asthma despite standard therapy
• Peak flow: May see improvement and less variability on biologics

Asthma Severity Classification

Severity	FEV1 or PEF	Symptoms
Intermittent	≥80%	≤2 days/week
Mild persistent	≥80%	>2 days/week
Moderate persistent	60-80%	Daily
Severe persistent	<60%	Throughout day

Stepping Up and Down Therapy

• Step up if: Not meeting control goals, frequent yellow/red zones
• Step down if: Well-controlled for 3+ months
• Peak flow guidance: Consistent green zone = consider step down
• Gradual: Step down one level at a time
• Monitor: Watch peak flow closely after any change

Asthma Control Assessment Tools

• ACT (Asthma Control Test): 5-question validated questionnaire
• ACQ (Asthma Control Questionnaire): 6-7 items including FEV1
• Peak flow role: Objective measure to complement symptoms
• Combined: Symptoms + peak flow = best assessment
• Goal: ACT ≥20, peak flow in green zone

School and Work Management

• Action plan: Provide copy to school nurse/workplace
• Peak flow meter: May keep at school/work
• Rescue inhaler: Should be accessible at all times
• Trigger awareness: Know triggers in environment
• Communication: Notify about asthma status

Travel with Asthma

• Peak flow meter: Pack in carry-on luggage
• Medications: Bring extra supply, carry-on preferred
• Action plan: Copy in multiple locations
• Altitude: May need adjustment at high altitude
• Air travel: Cabin air pressure generally safe

Preparing for Healthcare Visits

• Peak flow log: Bring record of daily readings
• Symptom diary: Note patterns, triggers, medication use
• Current medications: List with doses
• Questions: Write down questions in advance
• Action plan review: Update as needed

Final Memory Aids

• "Green = Go" - Continue normal routine
• "Yellow = Yield" - Slow down, take action
• "Red = STOP" - Emergency, get help
• "80-50 rule" - Zone cutoffs
• "Best of 3" - Always highest reading
• "Personal best beats predicted" - Use your own baseline

Peak Flow Monitoring Checklist

• ☐ Establish personal best when well-controlled
• ☐ Calculate zone cutoffs (80% and 50%)
• ☐ Check peak flow at same time daily
• ☐ Record best of 3 attempts
• ☐ Note symptoms and triggers
• ☐ Follow action plan based on zone
• ☐ Bring log to healthcare visits
• ☐ Update personal best annually

Final Safety Note

Peak flow monitoring is a valuable tool but should be used as part of comprehensive asthma management. If you are in the RED ZONE or experiencing severe symptoms (can't speak in full sentences, bluish lips, severe breathing difficulty), this is a medical emergency - use rescue inhaler and seek immediate medical attention or call 911. Always follow your personalized asthma action plan developed with your healthcare provider.

Final Reference Values

• Green zone: 80-100% of personal best
• Yellow zone: 50-80% of personal best
• Red zone: <50% of personal best
• Normal variation: <20% diurnal variation
• Bronchodilator response: ≥20% improvement significant
• Adult male range: 400-700 L/min typically
• Adult female range: 300-500 L/min typically

Peak Flow Meter Care

• Cleaning: Wash mouthpiece weekly with warm soapy water
• Drying: Allow to air dry completely before use
• Storage: Keep in clean, dry place
• Replacement: Per manufacturer guidelines (usually 1-2 years)
• Calibration: Cannot recalibrate - replace if inaccurate

Patient Education Points

• Peak flow is like a speedometer for your lungs
• It can detect worsening before you feel symptoms
• Personal best is YOUR target, not a population average
• Traffic light zones make decision-making simple
• Technique matters - get training from your provider
• Bring your meter and log to every asthma visit

Digital Peak Flow Monitoring

• Electronic meters: Automatic recording and trend analysis
• Smartphone apps: Log readings, track trends, set reminders
• Bluetooth meters: Sync directly with phone apps
• Sharing: Some apps allow sharing data with providers
• Trends: Visual graphs help identify patterns

Limitations of Peak Flow

• Effort-dependent: Poor technique gives poor results
• Large airway focus: May miss small airway disease
• Not diagnostic: Spirometry needed for diagnosis
• Normal doesn't rule out: Can have symptoms with normal PEFR
• Variability: Between devices and patient effort

Severe Asthma Warning Signs

• Peak flow <50%: RED ZONE - emergency
• No relief from rescue inhaler: Need emergency care
• Cannot speak full sentences: Severe obstruction
• Blue lips/fingernails: Cyanosis - emergency
• Drowsy or confused: Severe hypoxia
• Silent chest: Severe obstruction - little air moving

Clinical Workflow Summary

Establish personal best when well-controlled (2-3 weeks)
Calculate zone cutoffs (Personal best × 0.80 and × 0.50)
Monitor daily - same time, best of 3 attempts
Record in log with symptoms and triggers
Determine zone: Green (80-100%), Yellow (50-80%), Red (<50%)
Follow action plan based on zone
Contact provider if yellow zone doesn't improve
Seek emergency care if red zone or severe symptoms

Summary Table

• Purpose: Monitor airway obstruction
• Measure: Maximum expiratory flow (L/min)
• Technique: Best of 3 attempts
• Comparison: Personal best preferred over predicted
• Green: 80-100% - all clear
• Yellow: 50-80% - caution, take action
• Red: <50% - emergency

Peak Flow Calculator Final Summary

GREEN

80-100%

Continue routine

YELLOW

50-80%

Take action

RED

<50%

Emergency!

Final Disclaimer

This calculator provides estimated predicted peak flow values based on population equations. Individual results vary significantly. Always establish your personal best with proper technique during a period of good asthma control. Peak flow monitoring should be used as part of a comprehensive asthma management plan developed with your healthcare provider. If experiencing severe symptoms or in the red zone, seek immediate medical attention.

Comorbid Conditions

• Allergic rhinitis: Treat nose to help asthma control
• GERD: Reflux can trigger asthma symptoms
• Obesity: Weight loss can improve asthma control
• OSA: Sleep apnea worsens asthma
• Anxiety/depression: Can affect asthma perception

Lifestyle Modifications

• Smoking cessation: Essential for asthma control
• Weight management: Healthy weight improves lung function
• Exercise: Regular activity beneficial (with proper management)
• Stress management: Stress can trigger symptoms
• Sleep: Good sleep improves overall control

Environmental Control Measures

• Dust mites: Allergen-proof mattress covers, wash bedding weekly in hot water
• Pets: Keep out of bedroom, consider HEPA filter
• Mold: Control humidity, fix leaks, ventilate bathrooms
• Pollen: Keep windows closed during high pollen days
• Smoke: No smoking in home or car

Allergen Immunotherapy

• Allergy shots: Subcutaneous immunotherapy (SCIT)
• Sublingual tablets: For grass, ragweed, dust mite
• Duration: Typically 3-5 years of treatment
• Benefit: May reduce asthma symptoms and medication needs
• Selection: For allergic asthma patients with identified allergens

Types of Inhalers

• MDI: Metered-dose inhaler - most common, use with spacer
• DPI: Dry powder inhaler - breath-activated, no spacer needed
• SMI: Soft mist inhaler - slow-moving mist
• Nebulizer: Converts liquid to mist, for severe cases or young children
• Peak flow role: Check before and after inhaler to assess response

Quick Reference Values

• Green zone: 80-100% of personal best
• Yellow zone: 50-80% of personal best
• Red zone: <50% of personal best
• Diurnal variation: <20% is normal
• Bronchodilator response: ≥20% is significant
• Personal best: Highest over 2-3 weeks when well

Final Reference Card

• PEFR measurement: Best of 3 attempts, L/min
• Zone system: GREEN (80-100%), YELLOW (50-80%), RED (<50%)
• Personal best: Gold standard for comparison
• Action plan: Every patient needs written plan
• Emergency: Red zone = immediate action

Bronchial Thermoplasty

• Indication: Severe persistent asthma despite optimal therapy
• Mechanism: Radiofrequency reduces airway smooth muscle
• Procedure: Three bronchoscopy sessions
• Benefit: May reduce exacerbations and improve quality of life
• Peak flow: May see improved variability after procedure

Predictive Equations Overview

• Nunn & Gregg: Most widely used for adults
• EU/EN13826: European standard equations
• Godfrey: Commonly used for children
• Variables: Age, height, sex
• Limitation: Ethnicity not always accounted for

Clinical Decision Support

• GREEN zone action: Continue current medications, maintain routine
• YELLOW zone action: Use rescue inhaler, may need to increase controller, contact provider if no improvement
• RED zone action: Use rescue inhaler IMMEDIATELY, start oral steroids if prescribed, seek emergency care
• Documentation: Record readings, symptoms, and actions taken

Final Summary Reference

• Purpose: Monitor airway obstruction in asthma/COPD
• Units: Liters per minute (L/min)
• Best of 3: Always record highest reading
• Personal best: Preferred over predicted values
• Zone system: Traffic light approach for action
• Action plan: Essential for every asthma patient
• Technique: Standing, deep breath, blow hard and fast
• Frequency: Daily when stable, more often when ill
• Green: 80-100% - continue routine
• Yellow: 50-80% - take action
• Red: <50% - emergency
• Diurnal variation: <20% is normal
• BD response: ≥20% suggests reversibility
• Resources: ginasthma.org, lung.org

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