NIST Calibration Services Users Guide (SP 250) and its appendix identify three types of services available, “calibration services,” “measurement assurance programs (MAPs),” and “special tests.”  This appendix is intended to define the criteria required for each type of service.  See Section 5.20.11 for definitions of each type.

Criteria for Calibration Services or Measurement Assurance Programs (MAPs)

A service must conform to all of the following criteria in order to be listed in the SP 250 as a “calibration service” or “MAP”:
1. service is performed regularly with pre-established and well-defined conditions;
2. the measurement process is well-characterized and shown to be stable and predictable.  The variation in performance of individual devices being calibrated must not exceed pre-established limits (i.e., NIST calibrates only devices known to be suitable as reference or transfer standards);
3. quality assurance procedures (explicit) are in place and followed; and
4. thorough documentation and a long-range plan for the calibration service or MAP are available.
Laboratories may place additional requirements on the establishment of calibration services and MAPs

Criteria for Special Tests

Any service that meets one or more of the following criteria will be listed in the SP 250 as a “special test”:
1. the specific type of calibration is seldom requested, thus precluding the maintenance of a large statistical base for characterizing the measurement process;
2. the test requested is unique; or
3. the service is still under development (i.e., the measurement or calibration methods are still being perfected or the quality-assurance steps have not been completed).