Don't know that James will be following this thread 6 months later... so, replying for him, Rob:
The key is 'associated'. Labels can either be independent (dumb) or associative (smart - read data from an element).
See:
http://helpcenter.graphisoft.com/guides/archicad-17-int-reference-guide/documentation/annotation/lab...
although a typical workflow is to set up the default label (e.g., for slabs) here first:
http://helpcenter.graphisoft.com/guides/archicad-17-int-reference-guide/documentation/annotation/lab...
Then, you just tick the 'Label Slab' checkbox in the slab tool settings to have the associated label appear. Once the label is placed, it can be selected independently of the slab to customize its appearance (over the default) vs other slab associative labels.
In 17, you can specify if you want the top, bottom, or both elevations displayed, and if it is relative to the story or the project. See screenshot.
I'm not fond of this new 'dimension label' since it doesn't have a symbol associated with it, only text. But, the numbers are 'live', and respond to any changes to the slab thickness or vertical position.
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