A ringtest is part of an external quality assurance programme for a measuring method. Usually a reference institute sends identical samples which have to be analysed for special parameters to different laboratories. The industrial, medical or research laboratory gets a limited time with a deadline to send in the analysis results. The statistical evaluation and interpretation of the laboratories’ results is a great help for all participating labs as it opens the possibility to assess the quality of their analysis compared to other laboratories. For accredited laboratories (e.g. ISO 17025 etc.) the participation in ringtests is obligatory. Nevertheless, also non accredited labs take part in ringtests.