Guide 25 no longer exists and was the ISO/IEC Guide listing the requirements used to accredit calibration and testing labs. It has been officially replaced by ISO Standard 17025, which is much more detailed and will replace Guide 25 as a compliance document for accreditation of calibration labs over the next 2 years. You can contact someone at A2LA or NVLAP for details on meeting these requirements.
Ed Pritchard, Program Manager
Oak Ridge Metrology Center
a NVLAP Accredited Lab