Using Grafana with Osisoft PI

Hello Community,

i am using Grafana in combination with Osisoft PI as Datasource.
I am occuring some strange Problems that might be trivial though.

All PI-Tags (Values) can be seen in Grafana which is fine but i cant use Calculations to manipulate my Metrics.

what is the right way/Syntax to use Calculations ?

I hope anybody can help me there.