Module description: Systems biology research operates on multiple and large data sets. Repeatability of observation is important to guarantee the consistency and reliability of the analyses and conclusions. Changes in the observations are taken to reflect changes in the system and provide thereby primary tools to understand how the system works. Various procedures are applied in the research process to ensure repeatability. They include standardisation of measurements, calibration of measurement instruments, the application of protocols or detailed, written instructions to achieve repeatability of the performance of a measurement and the ensuing data analysis. Well-written protocols or SOPs (standard operating procedure) can be used to satisfy also other compliance requirements than those of systems biology. SOPs are for example recommended for procedures that involve the health and safety of patients.