When defining a trigger the threshold may vary on a per host basis due to some environmental differences. For example; the number of processors in an estate will vary and I may want to trigger a cpu load warning at system.cpu.num - 4.

I would then be able to define a trigger thusly:

{Template OS Linux:system.cpu.load[all,avg1].avg(5m)}>({Template OS Linux:system.cpu.num} - 4)

It should support at least + - * and /