AQL Sampling Inspection for PC Shipments: Sample Size, Defects and Acceptance

Task: accept a shipment of PCs without disputes

Acceptance of a PC shipment often turns into a dispute: the buyer finds defects, the supplier replies that these are isolated cases or that rules weren't agreed. Sampling inspection by AQL helps agree in advance on clear rules: how many devices to check, which defects are unacceptable and what decision will be made based on the result.

In plain terms, AQL is the acceptable quality level: the proportion of defects in a lot at which the lot is considered acceptable. It is not a promise that defects won't occur. It is a way to assess quality by sampling so the decision looks fair to both parties.

Sampling differs from 100% inspection in that you don't spend days testing every PC, but you reduce the risk of accepting an obviously defective lot. Full inspection is rarely needed: it's more expensive, slower and also doesn't guarantee absence of problems if tests are done formally or inspection conditions vary each time.

Typically one of the following decisions is made after inspection:

• accept the lot without remarks (defects are less than or equal to the allowable limit)
• accept with reservations (replace certain units, complete missing parts, repair)
• reject the lot (defects exceed the allowable limit)
• review the inspection (if there are doubts about lot homogeneity, packaging, documents or methodology)

Example: an office receives 200 identical PCs. They don't test all 200, but a pre-calculated sample. If the sample contains broken ports, unstable storage operation or mismatched configuration vs documents, these are recorded as defects of a certain class. The decision is then made by rules you can show the supplier.

AQL is not always appropriate. Choose a different approach when:

• the lot is small and it's simpler to check every unit
• a defect can lead to safety risks or stop critical processes
• there are signs of a systemic problem (identical failures across units)
• delivery is for equipment with strict requirements (e.g., medical devices, government infrastructure)
• there is no confidence the lot is homogeneous (different revisions, assemblies, production dates)

If the supplier has a mature quality system and clear documentation, disputes are easier. With a manufacturer or integrator responsible for the full lifecycle and support, it's easier to agree unified inspection criteria, report format and replacement procedure because responsibility processes are usually already described.

Preparation: documents, roles and lot boundaries

For AQL inspection to go smoothly, start not with percentages and tables but with rules. Most conflicts arise not from defects themselves but from parties having different understandings of what constituted the lot, under what conditions the inspection was performed, and which requirements were recorded in advance.

Identify the initiator and participants of the inspection. Usually the initiator is the buyer (quality service, IT or warehouse), but it's important to appoint a responsible person who makes on‑site decisions and signs documents. From the supplier's side it's useful to have a representative who confirms serial numbers, kit contents and the fact of unpacking. If the supplier doesn't attend, specify in advance that the inspection is done without them but with photo documentation and a report.

Record requirements in the contract, technical specification or annex. Be specific: model and configuration, allowable deviations (e.g., case scratches or fan noise), kit contents, packaging and labeling requirements, acceptance procedure and the time window to report nonconformities. If sampling acceptance is planned, state it explicitly, including defect category definitions.

Define lot boundaries in advance. For AQL a lot must be homogeneous: same model, configuration, build version and delivery conditions. If 300 PCs arrive but part have a different CPU or a different SSD batch, those are different lots and must be sampled separately. Otherwise the supplier can easily dispute results: “You mixed different items.”

Storage and unpacking conditions also affect results. If boxes were in a cold warehouse and you immediately powered on PCs in a warm room, condensation can cause false failures.

Before starting inspection, agree a short procedure:

• where and at what temperature the inspection is performed, and how long for acclimatization
• who opens packaging and how serial numbers are recorded
• what counts as a single unit (system unit, all‑in‑one, kit)
• how inspected units are separated from uninspected ones
• how remarks are recorded (report, photos, labeling boxes)

This preparation takes an hour but saves days of correspondence and reduces the chance of hearing: “The inspection conditions were wrong.”

How to choose AQL and inspection level for a PC lot

AQL (Acceptable Quality Level) is the percentage of defective units in a lot you are willing to accept based on sample inspection. AQL does not mean defects are “allowed.” It is a statistical threshold for deciding to accept or reject a lot.

Linked to AQL is LQ (Limiting Quality, sometimes LTPD) — the level at which a lot will almost certainly be rejected. If AQL is too lenient, the buyer bears the risk of receiving more problematic PCs. If it's too strict, the supplier will argue or add risk premiums to price and lead time.

The “inspection level” sets the sample size: the higher the level, the more units you check. For most PC deliveries the general level II is used as a balance. Level I is chosen when risk is low (repeat deliveries with stable statistics). Level III is used when the cost of error is high or incidents have occurred.

Acceptance numbers Ac/Re then apply: for the chosen sample size and AQL the table gives how many defects allow acceptance (Ac) and from which number rejection is required (Re). For example, if Ac=1 and Re=2, then 0–1 defects — pass; 2 or more — fail. Therefore define in advance which defects are considered the same and how to classify them.

AQL selection is often tied to downtime consequences:

• office PCs: tolerate looser cosmetic and packaging acceptance, but stricter on functionality
• workstations: stricter because user downtime is more costly
• servers: the strictest values and often a higher inspection level

To avoid disputes at acceptance, agree rules before inspection (ideally in the contract or appendix). Record:

• chosen AQLs and inspection level by defect categories (critical, major, minor)
• definitions of defects and how recurring issues are counted
• procedure for re‑sampling and handling disputes
• evidence format: photos, serial numbers, test results, packaging

For purchases for government bodies, banks or clinics where downtime is unacceptable, set stricter AQLs for critical and major defects and a reasonable allowance for minor defects.

Calculating sample size by AQL: step by step

To prevent disputes, calculate by the chosen AQL standard and record inputs. Then discussions with the supplier are about agreed rules, not impressions.

Step‑by‑step algorithm

First confirm what counts as the lot and the unit. For PCs it's usually “one system unit” or “a kit for one workplace.” If different models or configurations are in the delivery, do not mix them: each homogeneous group is assessed separately.

Next choose the inspection mode:

• normal — when the supplier is stable and previous deliveries were successful
• tightened — if there were defects/missing items, it's a new model, a new supplier or the delivery is critical
• reduced — only after a series of problem‑free acceptances and low risk

Using the AQL table find the code letter by lot size and inspection level, then the sample size for that code. Sampling must be random: don’t pick “top of the pallet” or “from the edge.” Record the selection method (for example, random box numbers).

Then use the same table to find Ac/Re for the chosen AQL. If defects in the sample are ≤ Ac, accept the lot. If defects are ≥ Re, reject the lot or switch to 100% inspection/rework — as pre‑agreed in the contract.

How to record the calculation in the report to avoid disputes

In the incoming inspection report one clear line with inputs and result is sufficient. Example: “Lot: 240 PCs, unit: 1 PC, inspection level: normal, AQL: 1.0 (major), table: (name/version), code letter: L, sample size: 50 pcs, Ac/Re: 1/2, selection method: random box numbers.”

This format makes the calculation verifiable: any party can open the same table and get the same numbers.

Which defects to treat as critical, major and minor

Classifying defects prevents acceptance becoming a subjective “like/dislike” debate. The more precisely you agree defect types and measurable signs, the easier it is for the supplier to accept findings.

Critical defects

Critical defects relate to safety and mandatory requirements. Often zero acceptance is set: even one case in a sample stops acceptance and triggers an investigation.

Examples: fire or electric shock risk, signs of overheating, damaged power cables, exposed conductors, missing mandatory labeling (serial number, conformity mark, power rating sticker). For high‑requirement sites you may also include document nonconformance on safety.

Major defects

Major defects are not necessarily dangerous but impair operation or mean the delivered configuration doesn't match the specification. Typical examples: unstable operation, spontaneous reboots, BIOS/UEFI errors, missing declared ports, different RAM or storage capacity than stated, non‑working network interface, driver issues for the declared OS.

For all‑in‑ones you may separately list touch and display: unresponsive touch zones, severe backlight non‑uniformity, excessive dead pixels beyond an agreed threshold.

Minor defects

Minor defects don't affect function but harm appearance or accounting: scratches, paint chips, scuffs, contamination, minor packaging damage, incomplete non‑mandatory documentation.

To prevent supplier disputes, formulate defects with measurable criteria:

• what is checked (component, parameter, document)
• how it's checked (visual, test, measurement)
• with what (checklist, test media, reference cable)
• threshold (e.g., “fails to boot 2 out of 2 attempts”)
• proof (photo, BIOS/UEFI screenshot, test log)

Below is an example working classification table.

What to check in each sampled unit: minimum set

In sampled inspection it's important to perform the same checks on every device in the sample. Then results look fair and repeatable, and the supplier has less room to argue.

1) Identification and external inspection

Start with what can be proven by photo and doesn't require powering on:

• serial number and label: match invoice and spec
• seals and signs of opening: tears, reseal, damaged screws, tool marks
• case and ports: cracks, dents, misalignment, loose connectors, damaged contacts
• marking: model, revision, power labels, warning stickers (if required)
• packaging: impact marks, wetting, re‑sealing

After inspection mark status: “accepted for functional testing” or “stopped due to critical defect.” If the defect is obvious (e.g., broken power jack), don't waste time with further tests on that unit.

2) Kit and conformity to specification

Check you received what you purchased. A common cause of disputes is “everything works but it’s not what we ordered.” Verify kit against contractual specification: power cable, adapters, Wi‑Fi antennas (if declared), mouse and keyboard (if included), documentation and warranty papers.

3) Quick functional test (10–15 minutes per PC)

The test set should be short but identical for all units:

• power on and boot: no errors or boot loops
• configuration: CPU, RAM size, SSD/HDD type and capacity, network adapter, Wi‑Fi/BT (if present)
• ports and network: at least USB, video output, wired network link up, sound (if required by spec)
• noise and temperature at idle: fans not “howling”, case not overheating on the desk
• software and licenses (if supplied): activate normally, version matches contract

A good practice is one inspection card per unit with fields for “fact” and “evidence” (photo of label, configuration screenshot).

Realistic example: acceptance of an office PC lot

An organization receives 200 office PCs. Deadlines are tight: workstations must be deployed within 5 business days, and the supplier asks to sign acceptance immediately to close shipment.

The team agreed rules in advance. They set AQLs: critical defects 0, major 1.0, minor 2.5. Inspection level — general II. For a lot of 200 the code letter was G, so the sample size was 32 PCs. Inspection was split into 2 days of 16 units each so the engineer and warehouse weren't overloaded.

Each sampled PC underwent the same checks: serial and kit against the invoice, external inspection, boot, BIOS check (CPU model, RAM, disk), short stability test, network and ports, OS activation (if supplied).

They found deviations in the sample:

• 1 PC doesn't power on, burning smell from power supply (critical: safety risk). Decision: that unit quarantined immediately, replacement requested, plus additional PSU checks on part of the remaining lot.
• 2 PCs have 256 GB SSDs instead of the declared 512 GB (major defect). Decision: record nonconformance and require SSD replacement or re‑supply.
• 3 PCs have noticeable case scratches (minor defect). Decision: accept with recorded remarks and agreed compensation or replacing elements if that matters to the buyer.

By AQL rules a single critical defect triggers rejection of the lot for criticals, even if other categories pass. To avoid a full dispute they formalized a “conditional acceptance”: the organization accepted the lot into storage but did not commission devices until the critical issue was resolved.

Agreements were recorded in the incoming inspection report: list of checked serials, test results, photos, defect classification and required actions with deadlines. The supplier signed the report and an action plan: replace 1 PC within 24 hours, provide SSD upgrades for 2 PCs within 2 days, and re‑inspect those units.

Common mistakes that cause supplier disputes

Disputes usually stem not from the defect itself but from inability to prove what was inspected: what exactly was checked, by which rules and which lot it belonged to.

1) Not defining the lot and mixing configurations

If the shipment contains different models, CPUs, RAM sizes, disk types or revisions, it's not one lot for sampling. If the sample is taken “from the whole pile,” the supplier can say: “You inspected a different configuration.”

Agree in advance: a lot equals the same configuration per spec plus a single delivery document (invoice/serial range) and one shipment. If several configurations exist, sample and report separately.

2) Inspecting things not specified in the spec

A common case: you check “as you used to” while the spec included concrete requirements (e.g., PSU interface, battery model, matrix type, TPM presence, kit cables). Then the supplier rightly says: “This wasn't in the contract.”

Before sampling prepare a short checklist based on the specification and contract annexes. Anything not documented should be recorded as a recommendation, not a defect.

3) Not recording serial numbers, seals and packaging condition

Without photos of serials and seals it's hard to prove a defect relates to a specific unit in the lot rather than occurring after unpacking. This is critical for disputes about “tampering,” “swap” or transport damage.

Minimum evidence:

• photo of device and box serial/label
• photo of seals before opening
• photo of packaging (especially corners and damage points)

4) Changing defect criteria during the inspection

If a deficiency was initially classed as “minor” and later reclassified as “major” or “critical,” it looks like result manipulation. The same applies if new inspection points are added mid‑process.

Agree the defect classification sheet before starting. If something unexpected appears, record it as a separate observation and decide its status separately, not retroactively.

5) No chain of custody for samples and results

Even with correct sample calculation a dispute arises if you can't prove which devices were sampled, who inspected them and where evidence is stored.

Maintain a simple chain of custody: list of sampled serials, signatures of responsible persons (who selected, who inspected), dates and storage location. For disputed units — separate tagging and prohibition on use until resolution.

How to document results so they are accepted without dispute

Suppliers usually dispute not the defect but how it was recorded. A good report reads as a set of verifiable facts: what was checked, by which rule, how and what was found.

What to include in the report

In the header include data that unambiguously ties the inspection to the delivery and sample:

• lot identifier: contract/invoice, PC model, quantity, serial ranges
• place and dates of inspection, conditions (e.g., 220V power, Ethernet available, test monitor)
• inspection committee: full names, positions, organizations, signatures
• methodology: AQL, inspection level, sampling plan, sample size, acceptance thresholds (Ac/Re)
• list of checks (brief) and tools used (e.g., test USB, disk utility)

Then add a table for each checked unit: serial number, result (OK/FAIL), defects found with classification.

How to describe a defect so it can't be misinterpreted

Describe defects with: fact + criterion + method + evidence. Avoid evaluative words like “bad,” “poor,” “suspicious.”

Example phrasing:

"PC S/N XXXXXX. On power‑up it fails POST: no display for 60 seconds. Test performed with known‑good monitor and cable (inv. №...), powered from a stabilized source. Repeated 3 times with identical result. Criterion: device must reach BIOS/OS screen within N seconds. Status: major defect (or critical per classification)."

If a defect concerns completeness, state “missing specific item” and reference the specification/invoice line, not “kit incomplete.”

Photo evidence and signatures

Photos should allow reconstruction without calls or explanations. Name and sign files so they match the report:

• label with serial and model
• general view of the PC and connections
• close‑up of the defect or screen with error message

File name can be simple: “date_lot_SNX_defect_item№”. In the report next to the defect list the photo numbers.

Decision on the lot: short and legally clear

At the end of the report record one decision and its conditions, without vague phrasing:

• accept the lot
• accept with reservations (list units/defects, replacement/repair deadlines, who and where performs work)
• reject the lot (reason: Re threshold exceeded or presence of critical defect)
• repeat inspection (when and under what conditions)

Ask the supplier's representative to sign the report on site. If they disagree, add a line “signature with remarks” and attach their written comments on a separate page.

Short checklist and next steps

Calm AQL acceptance rests on two things: agreeing rules in advance and then following them strictly. That way the supplier can accept remarks more easily and you can defend decisions internally.

Before starting ensure there is one agreed document with acceptance rules (or a contract annex) and a responsible person is appointed.

• Before inspection: AQL, inspection level, lot boundaries, Ac/Re tables, checklist and defect definitions recorded
• During inspection: random selection from the whole lot, marking inspected units, action log (date, who inspected, result)
• After inspection: report with sample results, photos, description of each defect, list of serial numbers for inspected devices, decision for each disputed unit
• Communication: one email with the outcome, reference to acceptance rules, defect counts by category and deadlines for fixes

Then act according to the chosen option. If the lot passes Ac/Re, complete acceptance and separately record single remarks that don't affect the decision. If it fails, avoid arguing “who's to blame” and keep the conversation factual: what doesn't conform, how it's proven and what action is required.

If procurement and deployment are turnkey, acceptance is often easier through a system integrator with clear responsibility and support. For example, GSE.kz (gse.kz) manufactures PCs and servers in Kazakhstan and provides 24/7 technical support through a service network, so inspection methodology and replacement/maintenance procedures are usually easier to formalize in advance and execute without protracted negotiations.