I created 'Zabbix aggregate' items:

grpsum["Home D","disk.io","last","0"]
grpsum["Home H","disk.io","last","0"]
grpsum["Home HM","disk.io","last","0"]

So far so good.

Then I created 'Calculated' item to sum them all:

grpsum["Home D","disk.io","last","0"]+grpsum["Home H","disk.io","last","0"]+grpsum["Home HM","disk.io","last","0"]

then I got error:

Format error or unsupported operator. Exp: [grpsum["HomeD","disk.io","last","0"]grpsum["HomeH","disk.io","last","0"]grpsum["HomeHOK

Is there any way to calculate agregated items?