A norm defines a set of tolerance thresholds that measurement results must meet according to the frequency with which samples are taken and the type of site. When a measurement exceeds one or more of these thresholds, an alert is generated.
- A parameter to which the threshold applies.
- Format, which specifies whether the threshold refers to a numeric value or a symbol
- The type of comparison, indicating how the measured value will be compared to the threshold.
- Threshold value.
- Monitoring programs and types of sites to which the threshold applies.
- Sampling periods (frequency at which measurements must be taken).
- Level of risk associated with exceeding the threshold.
A threshold must be entered for each value representing a limit. For example, the pH should be between 6 and 9.5. It is, therefore, necessary to enter a threshold to generate an alert when the pH result is less than 6 and a threshold when the pH is greater than 9.
Once the standard is active in the system, it is no longer possible to modify the comparison thresholds. Should a threshold change, an end date must be given to the standards in question so that the results no longer generate alerts. We can then duplicate the thresholds, modify them and thus create a new updated standard.