01 · Mechanics and boundaries
Mechanics and boundaries
A process flow chart represents the order of activities and decisions. Use a consistent symbol convention and define it for readers. Activity boxes describe actions; decision diamonds ask a question whose labeled branches determine the next route. Start and end markers establish the boundary. Arrows show sequence, not automatically material movement or elapsed time.
Choose a detail level that answers the question. A high-level map may contain release, pick, pack, check, and load. A diagnostic map needs stock holds, address queries, mismatch decisions, and return loops where those routes affect performance. Avoid mixing a broad stage with microscopic clicks unless the different detail has an explicit purpose.
02 · Construct the analysis
Construct the analysis
Follow actual orders and ask workers to narrate each trigger and completion condition. Write activities using a verb and object. Define each decision so different workers would choose the same branch for the same condition. Include all routes, even if an exception occurs rarely. Number steps to connect observation data to the map.
Validate the map by walking one normal and one exception case. Ensure every branch either reaches a defined end or returns through an explicit loop. Add processing and waiting annotations only after the sequence is stable. Separate current and proposed maps; otherwise an attractive future route may obscure the queue or workaround being investigated.
03 · Worked warehouse-dispatch example
Worked warehouse-dispatch example
The fictional North Quay warehouse dispatches a single parcel-order family. Its boundary starts when an order is accepted for release and ends at confirmed carrier handover. Demand is 240 orders in a 420-minute net working day. Each order contains three lines on average, but the example keeps the parcel order as the unit of flow. No number below describes a real organization or a demonstrated improvement. The purpose is to make the reasoning traceable rather than to present a success story.
A representative order spends 12 minutes awaiting release, 2 minutes being released, 18 minutes awaiting picking, 8 minutes being picked, 24 minutes awaiting packing, 5 minutes being packed, 10 minutes awaiting checking, 2 minutes being checked, 15 minutes awaiting loading, and 3 minutes being loaded. These mutually exclusive intervals total 99 minutes: 20 minutes of processing and 79 minutes of waiting. They describe one complete normal-route trace, not a statistically estimated mean for every order. A separate 100-order diagnostic sample contains 20 late orders, defined as handover more than 120 minutes after acceptance. The normal trace and late-order sample therefore answer different questions.
Three pickers, three packers, two checkers, and two loaders work in parallel within their respective stages. At the illustrated processing times, theoretical stage capacities are 157.5, 252, 420, and 280 orders per day. Picking is below the 240-order requirement even before interruptions or rework. Release has two staff and a theoretical capacity of 420. These capacities assume dedicated resources, identical order mix, and no overlapping assignments. They are not observed outputs and should never be reported as effective capacity.
The normal route is accept → release → pick → pack → check → load → confirm handover. A stock-available decision after pick initiation sends an unavailable line to a replenishment hold and then back to picking. A correct-order decision at checking sends a mismatch back to the appropriate correction stage. Neither branch can be represented faithfully as one uninterrupted forward chain.
In the 100-order sample, 12 orders take the replenishment route and 8 of those are late. The diagram places the hold before completion of picking, which tells the analyst where to collect its timestamps. The 99-minute normal trace excludes that exception. Adding an eight-minute hold to that trace would give 107 minutes only if no other waits change; it would not automatically explain crossing 120 minutes.
04 · Interpretation and decisions
Interpretation and decisions
Look for duplicated decisions, loops without exit criteria, activities with unclear completion, and queues hidden inside generic boxes. A map showing “handle issue” provides little basis for change until the triggering condition and return point are explicit. Use branch frequency and duration to decide where more detail is worth collecting.
A weak flow chart reproduces the written procedure without checking actual work. A sound chart distinguishes observed routes from mandated routes and discusses why workarounds exist. Do not delete an inconvenient exception from the picture to make flow look smooth; its frequency and consequence may make it the central analytical issue.
05 · Sound application and adaptations
Sound application and adaptations
For complicated systems, split the map into a main route and linked subprocesses with clear entry and exit conditions. Use a swimlane version when ownership is the issue; use a value-stream map when inventory and information release matter. Maintain identifiers across maps so data and discussion remain connected.
A flow chart alone cannot quantify variability, demonstrate causality, or identify the bottleneck. A densely detailed map can also become unreadable. Expand only the branches needed for a decision and retain a navigable overview. Version the map after changes and reobserve exceptions; a revised procedure does not ensure the revised route is what people actually follow.
06 · Evidence and follow-through
Evidence and follow-through
Make the observation auditable before debating a countermeasure. Preserve an anonymous order identifier, acceptance and handover timestamps, route, line count, shift, exception flag, and the observer's definitions. A timestamp from a completed screen action may describe data entry rather than physical completion. Reconcile several records with direct observation and ask the person doing the work what each event actually means. Keep an uncertainty note when clocks differ or two actions overlap; rounding cannot repair an ambiguous boundary.
Observe ordinary work and exceptions over a period that includes opening, replenishment, breaks, and the carrier cutoff. Selecting only easily followed orders produces a clean-looking but biased picture. When an order is unfinished at observation end, keep it visible as unfinished rather than silently deleting it. For multi-line orders, establish whether timing ends at the first line or the complete order. Include all three lines in the latter case, because the customer receives the order only after its final requirement is satisfied.
Turn the analysis into a bounded decision. Describe the proposed change, the mechanism expected to alter performance, the measure that would detect the change, and the conditions under which it would be withdrawn. A small layout change might reduce walking yet increase congestion; an extra release wave might lower one queue yet overload picking. Monitor handover performance, first-pass accuracy, work in process, and staff workload together. Treat the proposed numbers as planning assumptions until a comparable observation period supplies evidence.
07 · Boundary and robustness review
Boundary and robustness review
Before implementing the selected countermeasure, check the boundary one more time. If the analysis starts after order release, an upstream acceptance hold is outside its measured lead time even though the customer experiences it. If the analysis ends at the loading bay, a parcel waiting for the carrier is still incomplete within the stated dispatch outcome. Keep those events inside the customer-facing boundary, or state exactly why a narrower operational measure is also being used.
Assess robustness across normal variation. A proposed operating rule should specify what happens when an urgent order arrives, stock is unavailable, a staff member is absent, or the carrier changes collection time. Those conditions do not invalidate the main analysis; they define where its assumptions need adaptation. Rehearse an exception through the proposed route with the people responsible for each decision. Record which assumptions remain unverified and what evidence would be sufficient to proceed.
Finish with an explicit learning statement: what the evidence currently supports, what it does not establish, and which observation is needed next. A quantified hypothesis can be useful without becoming a guaranteed result. Retain the current-state observations so a later comparison can use the same event definitions and population. When the observed outcome differs from the prediction, revisit the mechanism and resource assumptions rather than adjusting the target after the fact.
Connections
Related methods and phase use
Placed under Analyze because of the outcome it supports. Use the method in other phases when its purpose and assumptions fit the work; the phase list is a guide to selection, not a compulsory sequence.
Sources
Professional foundations and further reading
The explanation and fictional teaching examples are written for LeanTrainingLab. Linked primary sources provide professional foundations; example values and local conventions are stated in the guide. The accepted toolset draws on Six Sigma+Lean Toolset, second edition (Lunau, editor; Springer, 2013). No book text or examples are reproduced here.