Background: There is a misunderstanding among users of C01 standards related to certification and calibration of testing equipment. In additions, certification of technicians and accreditation of laboratories are important aspects of the concrete industry. It would be helpful to the laboratories if C01had definitions of key terms related to certification and calibration. A series of definitions is proposed in four separate items that cover terms related to calibration of measuring instruments Some of the definitions are based on those in the ASTM Dictionary of Engineering Science and Technology with editorial modifications if deemed to be appropriate. Others are based on the International Vocabulary of Metrology--Basic and General Concepts and Associated Terms (VIM). Some are based on discussions with ARML (AASHTO Materials Reference Laboratory) staff. An attempt has been made to use easily understood language. This item passed in the December 2011 C01.91 subcommittee meeting by unanimous vote of members present. The ballot item wording is the same as balloted and approved by subcommittee C09.91 for use in ASTM C 125 Standard Definitions for Concrete. Terms related to calibration of instruments Rationale: There is a general misunderstanding of the process known as calibration, which is usually not necessary for the instruments used to make measurements on cement or cementitious specimens. In the international metrology community, calibration involves an assessment of measurement uncertainty. The term standardization is the appropriate term for most of the measuring instruments required in C01. This ballot item proposes definitions for these terms. Discussion is provided to help clarify the distinction between calibration and standardization.