What are the different levels of calibration?

There are typically four basic levels of calibration certificate. The level is determined only by the certificate, not supporting claims from other locations.

Non-compliant calibration

This type of calibration certificate is of little formal value, since it does not meet any compliance requirements, but may be sufficient for casual users. The certificate does not refer to an external laboratory accreditation body or ISO17025, it may reference ISO9001. These are commonly just pass / fail or QA certificates, with no test data. The calibration equipment is not traceable. The calibrated instrument is not traceable.

ISO 9001 compliant calibration

This type of calibration certificate meets the requirements of ISO9001. The certificate does not refer to an external laboratory accreditation body or ISO 17025, it may reference ISO9001. These certificates are commonly just pass / fail or QA certificates, with no test data. The calibration equipment is traceable. The calibrated instrument is not traceable.

ISO 17025 unaudited calibration 

This type of calibration certificate is more useful than the ISO9001 level, if good test data is attached. Successive test reports can be used to determine a rate of drift of the item, then calibration periods may be extended. The calibration certificate does not refer to an external laboratory accreditation body, and it references ISO17025. The calibration equipment is traceable. The calibrated instrument is not traceable.

ISO 17025 audited (traceable) calibration

This is the highest level of calibration certificate. The calibrated instrument is traceable, and can be used by anyone to calibrate other equipment in compliance with ISO 9001. When used by another audited laboratory, the calibrated instrument can be used to traceably calibrate other equipment. The calibration report includes full test data and uncertainty. The laboratory is externally audited by an accreditation organisation that operates within ISO/IEC 17011 and is an ILAC signatory. The calibration certificate must show the laboratory accreditation body logo, the laboratory accreditation number. and may optionally show the ILAC logo. The accreditation body will have a web site where the accreditation scope of the laboratory is available to the public. The calibration certificate is internationally recognised. 

Some National Measurement Institutes do not reference ISO 17025, but are at an equivalent level on the basis of peer review or other.