The Environment Agency has established its Monitoring     Certification Scheme (MCERTS) to deliver quality environmental measurements. The MCERTS product certification scheme provides for the certification of products according to Environment Agency performance standards, based on relevant CEN, ISO and National Standards. The MCERTS scheme is operated on behalf of the Environment Agency by Sira and is accredited by the United Kingdom Accreditation Service (UKAS) to ISO/IEC Guide 65:1996 'General requirements for bodies operating product certification systems'. The main benefit of MCERTS certified instruments to users is that they can be assured that the product complies with all regulations and requirements. The tests involve extensive laboratory and field trials including linearity, cross-sensitivity to other gases, response time, detection limit, zero and span drift, maintenance intervals and comparison with a standard reference method. The manufacturer's QA system is also assessed and regularly inspected to ensure that quality procedures are in place and being used effectively to provide product continuity.