The laboratory has a responsibility to ensure that sub-contractors who perform calibrations meet the requirements of the standard, just as if they were employees of the laboratory.

Accreditation to ISO/IEC 17025 or to ISO Guide 25 is evidence that a sub-contractor is competent.

Nevertheless, it is essential to be very clear in contractual arrangements with subcontractors, and in communications with them. Sub-contractors need to know all the relevant requirements of the laboratory, including criteria for acceptability of the equipment to be calibrated.