We can view these published limits, along with historical limits, by clicking the ‘View Published Limits’ button. The newest version (version 4 in the graphic) of the magnesium limits shows the new mean and standard deviation numbers, along with a historical record of previous limits for audit purposes. This screen highlights the change of numbers over time depending on the results obtained.
Looking at the test maintenance screen (below) we can see that the new 2σ and 3σ limits are now set against the magnesium test component. Future tests will use these new warning limits until the above process is repeated.
Using historical results to dynamically update test limits is a powerful feature to provide a warning of possible erroneous results and process drift in a quality control laboratory. This methodology can be used across manufacturing and environmental QC labs and is particularly prevalent in water QC laboratories.