Gauge about disk usage showing free in percentage and actual used GB at the same time?

Hello, i am new to Grafana. I am running Collectd with InfluxDB and Grafana 6.5.2 and i am trying build a Gauge for disk usage. It works fine if everything is percentage but i’ve seen screenshots that suggested it might be possible to have multiple values for it instead of percentage alone.

I would like to have the meter being the percentage but the label in center should be the remaining disk space (in GB) instead. When adding a second field, i am always ending up with a second Gauge.

I’ve seen it here:

Sadly this is a different issue and not explaining how to do this. Even more so the interface seem to have changed at some point. I don’t see any of these options when selecting Gauge.

This is my current query:

SELECT mean("value") FROM "df_value" WHERE ("type" = 'percent_bytes' AND "type_instance" = 'used') AND $timeFilter LIMIT 1

How to get the remaining space in GB to this query? Thanks allot for any help or suggestion.