I think this feature missing is a real pain. Why cannot zabbix calculate data for graphs. I know this can be circumvented by creating a calculated item. But this item is stored in DB and takes up space, its storage and retrieval affects disk performance. How simpler it would be, if we could just do Item1/Item2, or avg(item3) and instead of having to store the data twice, we just store item3 and calculate avg from that on the fly.