How to Choose a Calibration Lab in Singapore: 7 Questions to Ask Before You Sign

The Stakes of Choosing the Wrong Laboratory

The calibration certificate you receive from a laboratory is only as credible as the laboratory that issued it. A certificate from a non-accredited provider may look identical to one from a SAC-SINGLAS accredited laboratory (same format, same columns, same numerical results), but it carries a fundamentally different level of assurance. At an ISO 9001 or ISO 13485 audit, the auditor will ask to see your calibration certificates and may check whether the issuing laboratory holds current accreditation for the specific parameters being certified. An unaccredited certificate may not be accepted as evidence of traceable calibration, putting your entire measurement control system into question.

Singapore's calibration market includes dozens of providers: large SAC-SINGLAS accredited laboratories, smaller workshops offering calibration as an add-on service, and equipment dealers who provide "factory calibration" with their instruments. Understanding which type of provider is appropriate for your needs (and asking the right seven questions before committing), is the difference between a calibration programme that protects your quality system and one that only appears to.

This guide is structured around the seven questions you should ask any calibration laboratory before engaging their services. Each question is followed by an explanation of why it matters, what a good answer looks like, and what answer should raise a red flag. At the end, a summary decision framework table brings all seven together in a format you can use directly in your supplier evaluation process.

Question 1: Are You SAC-SINGLAS Accredited Under ISO/IEC 17025?

SAC-SINGLAS (Singapore Accreditation Council. Singapore Laboratory Accreditation Scheme) is Singapore's national laboratory accreditation scheme, operating under ISO/IEC 17025. Laboratories accredited under SAC-SINGLAS have been independently assessed to demonstrate technical competence, impartiality, and the ability to produce metrologically traceable calibration results. Their calibration certificates carry the SINGLAS mark and are internationally recognised under the ILAC Mutual Recognition Arrangement. Meaning they are accepted by accreditation bodies in over 100 countries.

When a laboratory says it is SAC-SINGLAS accredited, ask for: (a) the accreditation number, and (b) the date of the most recent surveillance assessment. You can verify both at the SAC website (sac.gov.sg). A laboratory that is reluctant to provide its accreditation number, or whose number does not appear on the SAC directory, is not accredited. Non-accredited laboratories can still produce calibration data, but they cannot independently verify their own traceability chain. They rely on the certificates of the reference standards they use, which may or may not be from accredited sources.

For ISO 9001:2015 clause 7.1.5.2(b), calibration must be performed "by a laboratory with competence in specific calibration activities, with traceability to International Measurement Standards." SAC-SINGLAS accreditation is the clearest and most auditor-defensible way to demonstrate this competence. A laboratory that is not accredited but claims to offer "traceable" calibration is shifting the verification burden onto you, and at an audit, that burden is real.

It is also worth noting that accreditation is maintained, not awarded once and forgotten. Accredited laboratories undergo annual surveillance assessments and periodic full re-assessments. A laboratory that was accredited three years ago but has since allowed its accreditation to lapse will not appear in the SAC directory as currently active. Always verify at the time of engagement, not at the time of your last engagement with the same laboratory.

Question 2: Does Your Scope of Accreditation Cover My Instruments?

This is the question that catches the most organisations out. SAC-SINGLAS accreditation is not a blanket certification that a laboratory can calibrate anything. It is awarded for specific measurement parameters (temperature, pressure, electrical, dimensional, mass, etc.) within specific ranges and with specific measurement uncertainties.

A laboratory may be accredited for temperature calibration in the range of -40°C to 1200°C but not for electrical calibration. If you send them a multimeter for calibration, they can calibrate it, but not under their accreditation. The resulting certificate will not carry the SINGLAS mark for the electrical parameters, even if the laboratory includes a SINGLAS logo on their letterhead. This is a compliance gap that an ISO auditor may identify and cite as a non-conformance.

Always ask the laboratory to show you their current Scope of Accreditation document. This lists, for each parameter, the measurement range covered and the measurement uncertainty achievable. Cross-reference this against your instrument list. If any instrument's parameter is not in the scope, you will need either a separate laboratory for that parameter or confirmation from the laboratory about how they handle out-of-scope instruments, and importantly, whether those out-of-scope calibrations will be clearly distinguished from accredited work on the certificates.

Some organisations maintain multiple laboratory relationships: one primary accredited laboratory for the majority of their instrument population, and specialist laboratories for outlier parameters. This is entirely normal and is a more honest approach than relying on a single laboratory to handle everything, including parameters outside their accreditation scope.

Question 3: Can You Calibrate My Instruments On-Site?

Some instruments cannot be moved to a laboratory for calibration. Large pressure testing rigs, fixed environmental monitoring systems, permanently installed sensors, and calibration frames for production jigs must be calibrated where they stand. Other instruments (large multimeters, installed thermocouples, building management sensors), can technically be moved but with significant disruption to operations.

An on-site calibration capability requires the laboratory to have portable calibration equipment that is itself calibrated and accredited, and engineers who are trained to operate in field conditions. The accuracy achievable in the field is often slightly lower than in a controlled laboratory environment, because the laboratory can control temperature, humidity, vibration, and electromagnetic interference in ways that a production floor or plant room cannot. For most production instruments, however, the difference is within acceptable limits and the practical benefits of on-site calibration (no instrument downtime from transport, no damage risk, no need to reconfigure systems after reinstallation), outweigh the small reduction in accuracy achievable.

Ask the laboratory three specific sub-questions: (a) do you carry out on-site calibration? (b) what instruments can you calibrate on-site? (c) are your on-site calibrations covered by your SAC-SINGLAS accreditation, or are they out-of-scope services? Some laboratories hold separate SINGLAS accreditation for on-site calibration activities; others do not. If on-site calibration is a significant part of your programme, verify that the on-site work is covered by the accreditation scope. A certificate from an on-site calibration conducted outside the laboratory's accreditation scope carries the same limitations as a certificate from a non-accredited laboratory, it is not independently assured.

Question 4: What Is Your Turnaround Time, and Your Realistic Queue?

For most in-laboratory calibrations, the standard turnaround in Singapore is 5–10 working days. Express turnaround (1–3 working days) is typically available at a premium of 30–100% on the standard fee. However, turnaround times are not fixed. They depend on the laboratory's current workload and queue.

During peak periods. Typically March–April and October–November, when many companies are completing their annual calibration cycles ahead of ISO surveillance audits. Turnaround times at busy laboratories can extend to 3–4 weeks. If you have a calibration due date driven by an audit schedule or an expiry date, a 4-week queue is a significant risk. A late calibration is a non-conformance; a lapsed calibration certificate at the time of audit is a more serious finding that may require investigation of all measurements made since the instrument's calibration expired.

When evaluating a laboratory, ask about their current average turnaround time and what their peak-season delays look like. A laboratory that can give you an honest answer ("currently 7 working days, can extend to 15 in peak season"), is being transparent about operational reality. One that always quotes 5 working days without qualification may be giving you a best-case number that does not reflect what you will actually experience. Building a 4–6 week lead time into your calibration scheduling, and submitting instruments well before their due dates rather than in the week before expiry, is the most reliable way to avoid last-minute extensions and the non-conformances they generate.

A practical scheduling approach used by well-run quality teams: treat the calibration due date as the last acceptable date for return, not the submission date. Work backwards by 4–6 weeks to set the submission date, and add a further buffer for any instrument that requires adjustment or that may need to go out-of-scope to a specialist provider. Instruments submitted on time and instruments with extension requests tell different stories at an audit.

Question 5: Do You Provide As-Found and As-Left Data on Your Certificates?

This question immediately separates accredited from non-accredited providers. An ISO/IEC 17025-compliant calibration certificate must include the as-found measurement data (the readings taken before any adjustment), as well as the as-left data taken after adjustment. The as-found data is critical for two reasons.

First, it tells you whether the instrument was in tolerance at the time of calibration. If it was out-of-tolerance as-found, you have an out-of-tolerance (OOT) situation and must investigate the impact of any measurements made since the last calibration. This is a formal quality management requirement under ISO 9001, ISO 13485, and most GMP frameworks. Without as-found data, you cannot make this determination. You do not know whether the instrument drifted out of tolerance yesterday or six months ago, and therefore you cannot bound the period of suspect measurements.

Second, as-found data over multiple calibration cycles tells you how the instrument is drifting, which is the empirical basis for adjusting calibration intervals. An instrument that is consistently found well within tolerance after 12 months may be a candidate for extending its calibration interval to 18 or 24 months. An instrument that approaches its tolerance limit every 12 months should perhaps be calibrated every 6 months. Without as-found data, interval decisions are made arbitrarily rather than from evidence, which is a weakness an auditor may note.

Non-accredited providers often issue certificates that show only the final result ("pass" or a post-adjustment measurement) without as-found data. This is insufficient for ISO 9001, ISO 13485, and GMP environments, and it makes interval management impossible. If a laboratory cannot or will not provide as-found data, this is a fundamental compliance gap, not a minor documentation issue.

Question 6: What Experience Do You Have in My Industry?

A SAC-SINGLAS accredited laboratory competent in electrical and mechanical calibration for general manufacturing may not be the best choice for pharmaceutical GMP calibration or for aerospace metrology. Industry-specific experience matters in three distinct ways.

First, different industries have different documentation requirements. GMP calibration records require specific format, including GMP-compliant language for OOT outcomes and adjustment records, formatted to satisfy FDA 21 CFR Part 11 or PIC/S guidelines. An experienced GMP calibration laboratory will know to include the phrases and data fields that an FDA or HSA inspector expects to see; a general-purpose laboratory may produce a technically correct certificate that fails format review and requires rework before it can be filed in the GMP records system.

Second, some industries use specialised instruments that require specialist knowledge and reference equipment: pharmaceutical validation temperature sensors (PT100/PT1000 probes in specific configurations for mapping studies), pressure transmitters with HART communication for process monitoring, or torque measurement systems for aerospace fastener assemblies. A laboratory with experience in your sector will have the right reference equipment and the right engineers with the right expertise. A laboratory encountering these instruments for the first time may not know how to configure them correctly for calibration, or may calibrate them in a way that does not represent their actual use condition.

Third, accredited laboratories serving specific industries often understand the regulatory context. They know which parameters are critical for your product release, which instruments need to be calibrated before each batch run versus annually, and which certificate formats are required by your regulatory submission. This context is hard to acquire quickly and makes a meaningful difference in how smoothly a calibration programme runs.

Ask the laboratory for references or case studies from your industry vertical. A laboratory serving pharmaceutical clients will be able to name clients (with permission) or describe the types of instruments they calibrate for GMP environments. A laboratory that claims to serve all industries without being able to give specific examples from yours may not have the depth of experience the claim implies.

Question 7: What Is Your Measurement Uncertainty for My Parameter, and Is It Adequate?

Measurement uncertainty is the quantified estimate of the spread of values that could reasonably be attributed to the measurement result. It is expressed at a specific confidence level (typically 95%, corresponding to a coverage factor k=2) and quantifies how well the laboratory's reference standard can determine the true value of the instrument under calibration. Every ISO/IEC 17025 certificate must include the measurement uncertainty for each measurement point. If a certificate does not include uncertainty, it is not compliant with ISO/IEC 17025.

The practical rule for calibration is the 4:1 test ratio (also called the test accuracy ratio or TAR). The laboratory's measurement uncertainty should be no more than one-quarter (1/4) of the tolerance you require the instrument to meet. This ratio ensures that the calibration result is reliable enough to make a meaningful pass/fail determination. If your instrument needs to be accurate to ±1°C, the calibration laboratory should have a measurement uncertainty of ±0.25°C or better for temperature at that range. If the laboratory's uncertainty is larger than 1/4 of your tolerance, their calibration cannot reliably determine whether your instrument is in or out of tolerance. You might receive a "pass" certificate for an instrument that is actually at or outside its tolerance limit, which negates the value of the calibration entirely.

Ask the laboratory to provide their measurement uncertainty for the specific parameter and range you need. Not a general claim about their capabilities, but a specific figure for your measurement scenario. A reputable accredited laboratory will have this in their Scope of Accreditation and can provide it on request before you commit to using their services. If a laboratory cannot provide a specific uncertainty figure, or if the uncertainty they provide exceeds the 4:1 threshold for your application, you should either seek a laboratory with better reference standards or renegotiate your instrument tolerance specifications with your quality team.

Summary: A Quick Decision Framework

The seven questions above translate into a straightforward evaluation framework. Use the table below when assessing any calibration laboratory in Singapore. Either as a new supplier or when reviewing an existing supplier at re-qualification time.

A laboratory that provides good answers to all seven questions is one that understands the compliance context you operate in, can demonstrate its technical competence independently, and has the operational capacity to support your programme reliably. The goal of a calibration programme is not simply to produce certificates. It is to ensure that your measurement system is fit for purpose and your quality records are defensible at audit. The right laboratory is the one whose capabilities genuinely match that goal.

If you are evaluating Unitest Instruments as a potential calibration laboratory, we hold SAC-SINGLAS accreditation (Acc. No. LA-2023-0845-C) covering electrical, temperature, and mechanical parameters. Our Scope of Accreditation is available for download, we provide as-found and as-left data on all accredited certificates, and our engineers regularly serve manufacturing, precision engineering, electronics, and regulated-industry clients across Singapore. We are happy to discuss your specific instrument list before you commit to engaging us.