ISO 8041:2005 specifies the performance specifications and tolerance limits for instruments designed to measure vibration values, for the purpose of assessing human response to vibration. It includes requirements for pattern evaluation, periodic verification and in-situ checks, and the specification of vibration calibrators for in-situ checks. Vibration instruments specified in ISO 8041:2005 can be single instruments, combinations of instrumentation or computer-based acquisition and analysis systems. Three levels of performance testing are defined in ISO 8041:2005: pattern evaluation, i.e. a full test of the instrument against the specifications defined in this International Standard; periodic verification, i.e. an intermediate set of tests designed to ensure that an instrument remains within the required performance specification, and in-situ checks, i.e. a minimum level of testing required to indicate that an instrument is likely to be functioning within the required performance specification.