4.21. In designing the monitoring programme, it should be considered whether the credibility of monitoring data needs to be verified by means of sufficient redundancy of information, independent verification of values, use of robust equipment and design, and, to the extent possible, use of natural analogues. For example, natural analogues can provide information for understanding the evolution of natural systems and material behaviour over long timescales (e.g. natural analogues exist for the corrosion of metals). This may help in the interpretation of the monitoring results, such as those relating to corrosion products in monitored water. It is also important, when considering monitoring of a given parameter, to clearly understand and communicate to the regulatory body and to interested parties what type of results would be expected and how the monitoring results will be interpreted. Ranges of expected values should be provided in order to assess uncertainties.