A South African business can have a scale that appears accurate and still face a compliance problem. A recent calibration report may show that the readings are close to known reference weights, but that report does not automatically permit the scale to be used for selling, buying, invoicing, or charging by weight. In the same way, a legally verified scale may still need separate calibration records for an ISO system, customer audit, production process, or internal quality programme.
The confusion exists because calibration and verification may involve similar equipment and tests. A technician may apply test weights, check zero, assess repeatability, and record errors during either service. The purpose and final decision, however, are different. Calibration measures and documents how the scale performs. Adjustment changes its response. Legal verification confirms whether an approved instrument meets the requirements for a prescribed use.
In simple terms, a scale used only for internal stock or production checks may need calibration without legal verification. A scale used to determine a commercial price, payment, or quantity may require legal verification. A business using the same scale for trade and quality control may need both services and two separate sets of records.
What Is the Difference Between Calibration and Legal Verification?
Calibration and verification answer different questions. Calibration asks, “How does this scale perform against known reference values?” Legal verification asks, “Does this individual scale comply with the legal requirements for its prescribed use?” Understanding that distinction prevents businesses from booking the wrong service or relying on the wrong certificate.
Calibration Measures and Documents Scale Performance
Scale calibration is a documented comparison between the indication shown by a scale and values provided by suitable reference standards. For a weighing instrument, the reference standards are usually calibrated weights selected for the scale’s capacity, readability, required accuracy, and normal operating range.
During calibration, the technician records how the instrument responds at selected load points. The results may show:
- The indicated weight
- The reference value
- The difference between them
- Repeatability results
- Eccentric or corner performance where included
- Correction values
- Measurement uncertainty
- The condition before and after any authorised adjustment
Calibration does not automatically mean that the technician changed the scale. Its first purpose is to establish and document performance. If the scale shows an unacceptable error, the customer may authorise an adjustment or repair, followed by another test. ISO/IEC 17025:2017 is the current international standard used to assess the competence, impartiality, and consistent operation of testing and calibration laboratories. A SANAS-accredited calibration therefore means more than placing a weight on a platform and checking the display. The laboratory must demonstrate competence for the calibration activity listed in its approved scope. That scope may limit the type of instrument, measurement range, location, method, and calibration capability covered by the accreditation.
Adjustment Changes the Scale
Adjustment is often confused with calibration, but it is a separate action. Calibration identifies the scale’s performance. Adjustment changes the scale so that its indication more closely matches the required value.
An adjustment may involve:
- Resetting zero
- Changing span settings
- Correcting linearity
- Adjusting individual load-cell corners
- Changing approved indicator parameters
- Correcting mechanical alignment
- Repairing or replacing faulty components
Calibration measures the error. Adjustment attempts to reduce the error. Once an adjustment has been made, the original calibration result no longer describes the scale’s current condition. The scale should therefore be tested again, and the records should clearly distinguish between as-found and as-left results.
The as-found result shows how the scale performed before work began. This matters during quality investigations because it can reveal whether earlier measurements may have been affected. The as-left result shows how the scale performed after authorised repair or adjustment.
Legal Verification Confirms Compliance
Legal verification is a compliance process for measuring instruments used for prescribed purposes. The National Regulator for Compulsory Specifications defines verification as determining whether an instrument complies with its type-approval requirements and is accurate within the tolerances prescribed by the Legal Metrology Act.
Verification may include checks of:
- Instrument make, model, and serial number
- Type-approval information
- Maximum capacity and minimum capacity
- Verification scale interval
- Required markings
- Approved software or indicator configuration
- Physical seals
- Installation condition
- Zero performance
- Repeatability
- Eccentric loading
- Errors at prescribed load points
- Maximum permissible errors
The result is a legal conformity decision. The instrument either meets the applicable requirements or it does not. A scale that fails must be repaired, adjusted, or otherwise corrected before it can receive a passing verification outcome.
Calibration vs Verification at a Glance
The following table shows the main differences without treating calibration and verification as competing services.
| Point of comparison | Calibration | Legal verification |
| Main question | How does the scale perform against reference values? | Does the scale meet the legal requirements for its prescribed use? |
| Primary purpose | Measurement assurance, traceability, quality control, and performance monitoring | Legal compliance for a prescribed measurement |
| Type of result | Numerical results, error, corrections, and uncertainty | Pass-or-fail conformity decision |
| Does it change the scale? | No, unless adjustment is separately authorised | Verification tests the scale presented; adjustment may be required before it passes |
| Is type approval always required? | No | Usually relevant where an approved instrument is required |
| Typical document | Calibration report or calibration certificate | Verification certificate and applicable seal or mark |
| Makes a scale legal for trade by itself? | No | Yes, where verification is required and the scale passes |
| Reports measurement uncertainty | Normally included in accredited calibration reporting | Not the main purpose of the verification result |
| Typical provider | Calibration service provider or accredited calibration laboratory | Designated verification body or NRCS where applicable |
A calibration certificate may include a statement that the scale meets a customer’s stated tolerance. That does not turn it into a legal verification certificate. The two decisions are based on different requirements and authority.
What Are the Roles of SANAS and the NRCS?
SANAS and the NRCS have connected roles in South Africa’s measurement system, but they are not the same organisation and do not perform the same function. Saying that SANAS personally calibrated or verified a customer’s scale is usually inaccurate. The service is performed by the laboratory or verification body.
SANAS Accredits Competence
The South African National Accreditation System is the country’s national body responsible for accreditation in conformity assessment. SANAS assesses whether an organisation has demonstrated competence for specific activities within a published scope.
SANAS maintains separate accreditation categories for organisations such as:
- Calibration laboratories
- Testing laboratories
- Inspection bodies
- Verification and repair bodies under legal metrology
- Certification bodies
- Medical laboratories
- Reference-material producers
Its public accredited-facilities database allows customers to review each organisation’s certificate and scope. The database separates calibration laboratories from legal-metrology verification and repair bodies, showing that these are distinct activities.
A SANAS logo on a website or document does not prove that every service offered by that organisation is accredited. Before accepting an accredited result, check whether the current scope covers:
- The relevant scale or instrument type
- The required capacity or measurement range
- The calibration or verification activity
- On-site work, if the scale was tested at your premises
- The named legal entity and facility
- The method or capability needed for your application
This is especially important for large platform scales, weighbridges, laboratory balances, and specialised weighing instruments. A provider may hold competence for one category or range without being accredited for every instrument it services.
The NRCS Administers Legal Metrology
The NRCS Legal Metrology unit administers activities required by the Legal Metrology Act and related regulations. Its responsibilities include type approval, market surveillance, verification, designation of private verification and repair bodies, and the assessment of verification officers and repairers. The Legal Metrology Act 9 of 2014 aims to maintain a legal measurement system that supports fair trade and protects public health, safety, and the environment. The NRCS may designate competent private organisations to verify or repair measuring instruments under legal-metrology control. These organisations work within defined fields and limits. The NRCS also provides verification where no designated body exists for a required service.
Does Your Scale Need Calibration, Verification, or Both?
The answer depends mainly on how the measurement is used. A scale’s appearance, price, capacity, or accuracy alone does not determine its legal status.
Start by asking:
- Does the weight determine what a customer pays?
- Does it determine what a supplier receives?
- Is a service charged according to weight?
- Does the weight appear on an invoice?
- Is the scale used only for an internal check?
- Does a customer or quality system require traceable calibration?
- Has the scale been repaired, adjusted, or moved?
- Is the instrument type approved for its intended application?
| Scale use | Calibration | Legal verification | Main action |
| Internal stock comparison | Often useful | May not be required | Define internal acceptance limits |
| Production or batch control | Usually appropriate | Depends on the use | Set a risk-based calibration schedule |
| Laboratory or quality-control weighing | Usually required by the quality system | Depends on the purpose | Confirm uncertainty and required range |
| Products sold by weight | Useful for monitoring | Usually required for prescribed trade | Confirm type approval and verification |
| Materials bought by weight | Useful | Usually required where prescribed | Check certificate and seal |
| Service charged by weight | Useful | May be required | Confirm the legal status before use |
| Trade scale included in an ISO programme | Usually needed | Required where prescribed | Keep both sets of records |
| Scale repaired or adjusted | Performance must be rechecked | Re-verification may be required | Assess the effect of the work |
| Scale moved to another site | Recalibration is sensible | Confirm verification status | Inspect installation before testing |
| Scale with unstable readings | Diagnosis is needed first | Verification is not fault-finding | Repair before final testing |
Scales Used for Internal Purposes
A scale used solely for internal stock monitoring, production checks, recipe control, or process comparison may not require legal trade verification. Calibration may still be essential because an incorrect internal result can cause waste, batch errors, stock discrepancies, or rejected products. The business should set its own documented acceptance limits based on the effect of an incorrect measurement. A warehouse scale used for approximate stock checks does not require the same level of measurement confidence as a laboratory balance used to prepare a sensitive formulation.
Internal use should be genuine. Calling a scale “for internal use” does not remove a legal requirement if its reading is later used to determine a sale price, payment, invoice quantity, or another prescribed result.
Scales Used for Buying, Selling, or Charging by Weight
Legal verification becomes relevant where the measurement affects a commercial transaction or another prescribed use. Common examples include:
- Meat, produce, bakery goods, or bulk food sold per kilogram
- Scrap material purchased by weight
- Agricultural products bought by mass
- Laundry services charged by measured weight
- Industrial material invoiced according to quantity
- Freight charges based on measured mass
- Public or commercial weighing services
For such applications, the business may need a correctly type-approved scale, legal verification of the individual instrument, intact seals, and current verification documentation. Scales4U states that industries trading over a scale require verified equipment. Our verification service covers eligible type-approved scales up to 4,000 kg and includes verification documentation.
Scales Used for Trade and Quality Control
Some businesses need both calibration and legal verification. A food processor, manufacturer, recycling facility, or warehouse may use a verified scale to determine commercial quantity while also including that instrument in an ISO, customer, or internal calibration programme.
In that situation:
- Verification supports legal use.
- Calibration supplies technical performance data.
- Maintenance keeps the instrument stable.
- Repair corrects faults.
- Adjustment changes inaccurate settings.
- Separate records show which activity was performed.
The calibration certificate does not replace verification, and the verification certificate may not provide all the uncertainty, traceability, and as-found data required by a quality auditor.
What Happens During Calibration and Verification?
The exact procedure depends on the scale, range, method, and legal requirements. Still, understanding the normal sequence helps a customer prepare the equipment and recognise whether the correct service was completed.
Typical Scale Calibration Process
A professional calibration commonly follows these steps:
- Identify the scale. The technician records the make, model, serial number, capacity, readability, location, and intended use.
- Inspect the condition. The platform, indicator, level, cables, load cells, power supply, and environment are checked for faults that could affect the result.
- Confirm zero and stability. The scale must settle and return to zero correctly before meaningful testing begins.
- Record as-found performance. Results are taken before adjustment or repair.
- Apply reference weights. Suitable traceable weights are placed at selected points across the useful range.
- Check repeatability. The same load may be applied several times to assess consistency.
- Check eccentric loading where required. The load is placed at different positions to assess corner or platform variation.
- Calculate error and uncertainty. The indication is compared with the reference value.
- Compare against customer limits. This is done where acceptance criteria have been agreed.
- Adjust only with authorisation. Any change should be recorded separately.
- Retest the scale. As-left results are recorded after adjustment.
- Issue the report or certificate. The document should identify the work completed and the results.
The number of test points should not be copied from a generic checklist. It should reflect the scale’s normal range, resolution, risk, method, and customer requirements.
Typical Legal-Verification Process
Legal verification focuses on conformity with the requirements for the prescribed instrument and use. A typical process includes:
- Confirming the instrument identity
- Checking its type-approval details
- Inspecting required markings
- Confirming the approved configuration
- Inspecting seals and controlled settings
- Checking installation and operating condition
- Performing prescribed weighing tests
- Comparing errors with maximum permissible limits
- Recording a pass-or-fail decision
- Applying verification evidence when the instrument passes
- Issuing the verification certificate
Although the technician may use weights and tests similar to those used during calibration, verification does not simply issue a general accuracy report. It determines legal conformity.
Correct Sequence for an Inaccurate Scale
A scale with unstable, drifting, or clearly incorrect readings should be inspected before final verification.
The practical sequence is:
Inspect → record the as-found condition → repair or adjust → retest or calibrate → verify where required
Possible causes that should be corrected first include:
- Damaged load cells
- Loose or unstable platforms
- Poor leveling
- Mechanical binding
- Junction-box faults
- Indicator damage
- Cable problems
- Moisture ingress
- Incorrect settings
- Foundation movement
Booking verification alone will not repair these faults.
When Must the Scale Be Checked Again?
A calendar date is important, but it should not be the only trigger for calibration, inspection, or re-verification. A scale can lose accuracy before its planned service date because of damage, movement, environmental exposure, or heavy use.
Set Calibration Intervals According to Risk
Calibration frequency should be based on:
- Frequency of use
- Scale capacity and readability
- Required process tolerance
- Previous calibration history
- Known drift
- Value of the product being weighed
- Effect of an incorrect result
- Temperature and humidity
- Vibration
- Washdown conditions
- Overload risk
- Customer requirements
- Quality-system procedures
- Manufacturer guidance
A lightly used warehouse scale may remain stable for a longer period than a scale exposed to daily washdown, forklift impact, or continuous production loading. The business should review previous results and shorten the interval if the instrument regularly approaches or exceeds its acceptance limit.
Do Not Wait for the Due Date After a Significant Change
Arrange an inspection or service after:
- Relocating the scale
- Replacing a load cell
- Replacing the indicator
- Breaking a seal
- Adjusting the scale
- Repairing the platform
- Exposing the equipment to water
- Overloading the scale
- Striking it with a forklift
- Finding unstable readings
- Receiving a customer complaint
- Failing an internal accuracy check
The exact action may be repair, adjustment, calibration, re-verification, or a combination of these services.
What Happens When a Scale Fails?
A failed result should lead to a documented response rather than a quick adjustment with no investigation.
A useful process is:
- Record the as-found error.
- Decide whether the scale should remain in use.
- Diagnose the cause.
- Repair or adjust the instrument.
- Retest it.
- Calibrate where required.
- Complete legal re-verification where required.
- Review earlier measurements that may have been affected.
- Record corrective action.
The historical review is important where the scale influenced invoices, batches, customer quantities, or supplier payments. The business should consider the size and direction of the error, when the scale last passed a check, and which records may be affected.
Which Scales4U Service Should You Book?
The correct service depends on the scale’s use and present condition. Providing the make, model, capacity, serial number, location, and intended use helps the service team identify the right next step.
Book Calibration for Measurement Evidence
Calibration is appropriate where the business needs:
- Internal quality records
- Measurement traceability
- ISO or customer audit evidence
- Accuracy monitoring
- Drift detection
- Post-repair results
- As-found and as-left data
- Process acceptance decisions
Scales4U provides calibration services at customer sites and at its premises, with a calibration report supplied after the service.
Book Legal Verification for Eligible Trade Scales
Verification is relevant where a type-approved scale is used for a prescribed commercial purpose, including buying, selling, invoicing, or charging according to measured weight. Scales4U verify eligible type-approved scales up to 4,000 kg, with verification documentation after the process.
Book Inspection or Repair for Unstable Readings
Start with inspection or repair where the scale:
- Does not return to zero
- Shows different readings for the same load
- Has a damaged load cell
- Has been struck or overloaded
- Has moisture inside the indicator or junction box
- Has loose cables
- Rocks on the floor
- Produces fluctuating results
- Has damaged seals or controls
Scales4U also provides maintenance & repairs, and service-level agreements with planned visits based on customer requirements.
Final Thought
SANAS calibration and legal verification support accurate weighing in different ways. Calibration provides measured evidence of scale performance, error, traceability, and uncertainty. Adjustment changes the scale when correction is needed. Verification confirms whether an approved instrument meets the legal requirements for its prescribed use.
A scale used for internal monitoring may need calibration only. A scale used to determine a commercial price, payment, or quantity may require legal verification. A business operating under both trade and quality requirements may need separate calibration and verification records. Before booking a service, identify how the weight is used and whether the scale is stable, damaged, repaired, or recently moved. Scales4U can assess the instrument and help determine whether the correct next step is calibration, maintenance, repair, legal verification, or a planned service agreement.
