Grafana add up metrics from same source but different dimensions - Netdata

Hi,
I have the problem that metrics from the same source but with different dimensions can’t be added up, subtracted or …etc.

netdata_system_ram{chart="system.ram",family="ram",dimension="used"}
+netdata_system_ram{chart="system.ram",family="ram",dimension="free"} 

Can’t be processed, while something like:

netdata_system_ram_used{chart="system.ram",family="ram"}
+netdata_system_ram_free{chart="system.ram",family="ram"}

would work.

Both statements would result in a single metric with 1 value.

netdata_system_ram{chart="system.ram",family="ram",dimension="used"}

netdata_system_ram_used{chart="system.ram",family="ram"}

I have attached an image, with the top not being able to be added up and the bottom being able to be added up.