There really shouldn’t be anything special to make this work. The Number:Temerature Items need to be tagged with “Measurement” for the point and “Temperature” for the property. These Items need to be a member of a Location or a member of an Equipment that is a member of a Location.
That’s all that’s needed.
For the trend line, by default, the trend line appears on stand alone widgets for Number Items. On the Properties tab of the overview page there is also an “Analyze All” button at the bottom of a given card.
I’m unaware of a way to make the trend line appear in a list item widget (i.e. those widgets shown on the Locations and Equipment tabs of the overview page.
As for manual, It doesn’t really address your first question directly because it mostly just happens. But the relevant docs include:
- Semantic Model | openHAB
- Pages - Overview Page | openHAB (has a section for the charting and customizing the badges that appear on the Locations cards)
- oh-label-card - Label Card | openHAB (shows how to configure the trendline if you choose to create a custom widget)
A Deep Dive into the Semantic Model provides some more detail on how the semantic model works.