Calculate total power consumption to date

[hsv]

Hi
I can get the current watt used every sec from a SNMP request.
I would like to add this up. Something like this
WattTotalKWh=WattTotalKWh+WattNow/1000/3600

But how do I do this. I have looked at calculated Items, but I cannot see how I an get it to work.

So is it possible to create a global variable add to this variable.

Regards
Henning

[Singularity]

We can make a calculated item and in its formula we can do something like .... last("Visible_host_name:key") + last("Visible_host_name:key)