We notice a small problem on the Calculated Item documentation of Zabbix 3.0, in every example of "last" function the parameter1 is not reported.
As i remember before zabbix 2.2 release this parameter was an option but since 2.2 is a requirement (I have tested on Zabbix 3.0).
Could you update the documentation to reflect this requirement?

Ref.https://www.zabbix.com/documentation/3.2/manual/config/items/itemtypes/calculated
Example:

Use of function last:
100*last("vfs.fs.size[/,free]")/last("vfs.fs.size[/,total]")