I have Kitchen.temp (key: temp28cc222a050000d9) populated by trap.
I have created several calculated items based on that, but only count works fine:
Kitchen.temp.avg: avg("Zabbix server:temp28cc222a050000d9",10)
Kitchen.temp.avg_man: sum("Zabbix server:temp28cc222a050000d9",10)/count("Zabbix server:temp28cc222a050000d9",10)
Kitchen.temp.count: count("Zabbix server:temp28cc222a050000d9",10)
Kitchen.temp.sum: sum("Zabbix server:temp28cc222a050000d9",10)