we make a template for a calculated item by name of CalcTem01 like this: last(IFOut)+last(IFIn)
a host with name of Cis01 linked to CalcTem01 and it gets the appropriate template items
but we must manually add name of host to that inherited items like this: last(Cis01:IFOut)+last(Cis01:IFIn)
then the calculated item get result and work truly
we also try the last(CalcTem01:IFOut)+last(CalcTem01:IFIn) in template,but zabbix not change the host name of CalcTem01 to Cis01

by this definition, template-based design for calculated item not work true