Regarding the Line weight Settings in Revit, this was provided to "Archman" (member username), a member of AUGI, in July of 2006 at AUGI by Autodesk support and David Conant confirmed its accuracy.
The question had to do with the logic of defining line weights and the various scales present in the Lineweights dialog. Specifically, "What line weight(s) does Revit use when you use a scale that isn't defined there?"
Autodesk Support wrote:
In this case the line weights will be assigned to the last lineweight before it until the lineweight can be rounded to the next one. For example: between 1/16" = 1' and 1/32" = 1'. If you only have these two weights defined at scale and none of the increments inbetween then 1" -20' and 3/64"= 1' will default to the 1/16= 1' setting while 1" = 30' feet will round up to 1/32" =1' . Any of the line weights after the last defined scale will default to the last defined scale.
To add to this, when a scale is not defined, and a view is plotted that uses it, and it falls in between two that are, Revit will use the next largest scale.
To summarize, it uses the closest or larger scale depending on the proximity to the defined scales and it uses the corresponding lineweight settings.