Calculated and Aggregate Information
Through an arithmetic expression, calculated items allow to create virtual data sources, where the values are periodically recalculated. The result is stored, allowing to generate graphs, alarms or send notifications.
An example of a calculated item would be to calculate the sum of traffic between two ports on a network switch.
With hosts being organized into groups you can create items with aggregate functions like maximum, minimum and average of an item that is common to all hosts in the group.
An example of an aggregate item would be to calculate the average of memory usage across all hosts of a specific group.